From University of Minnesota Twin Cities: “Comet Catalina suggests comets delivered carbon to rocky planets”

From University of Minnesota Twin Cities

March 5, 2021

Rhonda Zurn
College of Science and Engineering, Twin Cities
612-626-7959
rzurn@umn.edu

This illustration of a comet from the Oort Cloud as it passes through the inner solar system with dust and gas evaporating into its tail. SOFIA’s observations of Comet Catalina reveal that it’s carbon-rich, suggesting that comets delivered carbon to the terrestrial planets like Earth and Mars as they formed in the early solar system. Credit: NASA/DLR SOFIA/Lynette Cook.

In early 2016, an icy visitor from the edge of our solar system hurtled past Earth. It briefly became visible to stargazers as Comet Catalina before it slingshotted past the Sun to disappear forevermore out of the solar system.

Among the many observatories that captured a view of this comet, which appeared near the Big Dipper, was the Stratospheric Observatory for Infrared Astronomy (SOFIA), NASA’s telescope on an airplane.

NASA/DLR SOFIA modified Boeing 747 aircraft.

Using one of its unique infrared instruments, SOFIA was able to pick out a familiar fingerprint within the dusty glow of the comet’s tail—carbon.

Now this one-time visitor to our inner solar system is helping explain more about our own origins as it becomes apparent that comets like Catalina could have been an essential source of carbon on planets like Earth and Mars during the early formation of the solar system.

New results from SOFIA, a joint project of NASA and the DLR German Aerospace Center, were published in the Planetary Science Journal.

“Carbon is key to learning about the origins of life,” said the paper’s lead author, Charles “Chick” Woodward, an astrophysicist and professor in the University of Minnesota Twin Cities Minnesota Institute of Astrophysics. “We’re still not sure if Earth could have trapped enough carbon on its own during its formation, so carbon-rich comets could have been an important source delivering this essential element that led to life as we know it.”

Frozen in Time

Originating from the Oort Cloud at the farthest reaches of our solar system, Comet Catalina and others of its type have such long orbits that they arrive on our celestial doorstep relatively unaltered.

Milky Way Galaxy from Sun to Interstellar Space beyond the Oort Cloud. Credit: NASA/ JPL-Caltech.

This makes them effectively frozen in time, offering researchers rare opportunities to learn about the early solar system from which they come.

SOFIA’s infrared observations were able to capture the composition of the dust and gas as it evaporated off the comet, forming its tail. The observations showed that Comet Catalina is carbon-rich, suggesting that it formed in the outer regions of the primordial solar system, which held a reservoir of carbon that could have been important for seeding life.

While carbon is a key ingredient of life, early Earth and other terrestrial planets of the inner solar system were so hot during their formation that elements like carbon were lost or depleted. While the cooler gas giants like Jupiter and Neptune could support carbon in the outer solar system, Jupiter’s jumbo size may have gravitationally blocked carbon from mixing back into the inner solar system.

Primordial Mixing

So how did the inner rocky planets evolve into the carbon-rich worlds that they are today?

Researchers think that a slight change in Jupiter’s orbit allowed small, early precursors of comets to mix carbon from the outer regions into the inner regions, where it was incorporated into planets like Earth and Mars.

Comet Catalina’s carbon-rich composition helps explain how planets that formed in the hot, carbon-poor regions of the early solar system evolved into planets with the life-supporting element.

“All terrestrial worlds are subject to impacts by comets and other small bodies, which carry carbon and other elements,” Woodward said. “We are getting closer to understanding exactly how these impacts on early planets may have catalyzed life.”

Observations of additional new comets are needed to learn if there are many other carbon-rich comets in the Oort Cloud, which would further support that comets delivered carbon and other life-supporting elements to the terrestrial planets. As the world’s largest airborne observatory, SOFIA’s mobility allows it to quickly observe newly discovered comets as they make a pass through the solar system.

SOFIA is a joint project of NASA and the DLR German Aerospace Center. NASA’s Ames Research Center in California’s Silicon Valley manages the SOFIA program, science, and mission operations in cooperation with the Universities Space Research Association, headquartered in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart. The aircraft is maintained and operated by NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California.

See the full article here .

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The University of Minnesota, Twin Cities (often referred to as the U of M, UMN, Minnesota, or simply the U) is a public research university in Minneapolis and Saint Paul, MN. The Twin Cities campus comprises locations in Minneapolis and St. Paul approximately 3 miles (4.8 km) apart, and the St. Paul location is in neighboring Falcon Heights. The Twin Cities campus is the oldest and largest in the University of Minnesota system and has the sixth-largest main campus student body in the United States, with 51,327 students in 2019-20. It is the flagship institution of the University of Minnesota System, and is organized into 19 colleges, schools, and other major academic units.

The University was included in a list of Public Ivy universities in 2001. Legislation passed in 1851 to develop the university, and the first college classes were held in 1867. The university is categorized as a Doctoral University – Highest Research Activity (R1) in the Carnegie Classification of Institutions of Higher Education. Minnesota is a member of the Association of American Universities and is ranked 14th in research activity, with $881 million in research and development expenditures in the fiscal year ending June 30, 2015.

University of Minnesota faculty, alumni, and researchers have won 26 Nobel Prizes and three Pulitzer Prizes. Notable University of Minnesota alumni include two vice presidents of the United States, Hubert Humphrey and Walter Mondale.

From Harvard-Smithsonian Center for Astrophysics: “The Sun May Have Started Its Life with a Binary Companion”

From Harvard-Smithsonian Center for Astrophysics

August 18, 2020

Amy Oliver
Public Affairs
Center for Astrophysics | Harvard & Smithsonian
Fred Lawrence Whipple Observatory
520-879-4406
amy.oliver@cfa.harvard.edu

Artist’s conception of a potential solar companion, which theorists believe was developed in the Sun’s birth cluster and later lost. If proven, the solar companion theory would provide additional credence to theories that the Oort cloud formed as we see it today, and that Planet Nine was captured rather than formed in place.Credit: M. Weiss

A new theory published today in The Astrophysical Journal Letters by scientists from Harvard University suggests that the Sun may once have had a binary companion of similar mass. If confirmed, the presence of an early stellar companion increases the likelihood that the Oort cloud was formed as observed and that Planet Nine was captured rather than formed within the solar system.

Dr. Avi Loeb, Frank B. Baird Jr. Professor of Science at Harvard, and Amir Siraj, a Harvard undergraduate student, have postulated that the existence of a long-lost stellar binary companion in the Sun’s birth cluster—the collection of stars that formed together with the Sun from the same dense cloud of molecular gas—could explain the formation of the Oort cloud as we observe it today.

Oort Cloud, The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA, Universe Today

Popular theory associates the formation of the Oort cloud with debris left over from the formation of the solar system and its neighbors, where objects were scattered by the planets to great distances and some were exchanged amongst stars. But a binary model could be the missing piece in the puzzle, and according to Siraj, shouldn’t come as a surprise to scientists. “Previous models have had difficulty producing the expected ratio between scattered disk objects and outer Oort cloud objects. The binary capture model offers significant improvement and refinement, which is seemingly obvious in retrospect: most Sun-like stars are born with binary companions.”

If the Oort cloud was indeed captured with the help of an early stellar companion, the implications for our understanding of the solar system’s formation would be significant. “Binary systems are far more efficient at capturing objects than are single stars,” said Loeb. “If the Oort cloud formed as observed, it would imply that the Sun did in fact have a companion of similar mass that was lost before the Sun left its birth cluster.”

More than just redefining the formation of our solar system, evidence of a captured Oort cloud could answer questions about the origins of life on Earth. “Objects in the outer Oort Cloud may have played important roles in Earth’s history, such as possibly delivering water to Earth and causing the extinction of the dinosaurs,” said Siraj. “Understanding their origins is important.”

The model also has implications for the hypothesized Planet Nine, which Loeb and Siraj believe isn’t alone out there. “The puzzle is not only regarding the Oort clouds, but also extreme trans-Neptunian objects, like the potential Planet Nine,” said Loeb. “It is unclear where they came from, and our new model predicts that there should be more objects with a similar orbital orientation to Planet Nine.”

Both the Oort cloud and the proposed location of Planet Nine are so distant from the Sun that direct observation and assessment are challenging for today’s researchers. But the Vera C. Rubin Observatory, which sees first light in early 2021, will confirm or deny the existence of Planet Nine and its origins. Siraj is optimistic, “If the VRO verifies the existence of Planet Nine, and a captured origin, and also finds a population of similarly captured dwarf planets, then the binary model will be favored over the lone stellar history that has been long-assumed.”

If the Sun did have an early companion that contributed to the formation of the outer solar system, its current absence begs the question: where did it go? “Passing stars in the birth cluster would have removed the companion from the Sun through their gravitational influence,” said Loeb. “Before the loss of the binary, however, the solar system already would have captured its outer envelope of objects, namely the Oort cloud and the Planet Nine population.” Siraj added, “The Sun’s long-lost companion could now be anywhere in the Milky Way.”

See the full article here .

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The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

From Asgardia via Medium: “Which Spacecraft Will Reach Interstellar Space Next?”

From Asgardia

via

Medium

NASA’s Voyager 2spacecraft reached interstellar space in December 2018, following in the footsteps of its sister, Voyager 1. Currently, only five spacecraft have been launched that can make such a grand exit, including the Voyagers. The other three are Pioneers 10 and 11, and New Horizons. Which one will make a great escape next?

NASA/Voyager 2

NASA/Voyager 1

NASA Pioneer 10

NASA Pioneer 11

NASA/New Horizons spacecraft

Reaching interstellar space is a milestone that is thought of as leaving the solar system by a specific definition. In 1990, the New York Times reported that Pioneer left the solar system when it flew past Neptune’s orbit. But that’s not what Voyager 2’s scientists used as their definition. Instead, the more recent measurements said the crossing of the sun’s heliopause, the theoretical boundary to its heliosphere, is the determining factor for entering interstellar space.

Heliopause https://galnet.fandom.com/wikiHeliopause

The heliosphere is a bubble of charged particles that are created by and flows past the sun. It is used by scientists to mark where interstellar space starts.

NASA Heliosphere

However, the heliosphere is tricky, and there are many changes such as the sun’s 22-year solar cycle, the shrinking and growing with the solar wind, and stretching out behind the sun in the star’s direction of travel. It’s not something that can be measured easily from Earth. Thus, NASA’s Interstellar Boundary Explorer (IBEX) mission is trying to define the edges of the bubble remotely.

Observations from the Voyager probes’ indicate that they’ve pierced this bubble. However, since researchers think the Oort Cloud also surrounds the sun, an area of icy bodies that is estimated to stretch from 1,000 to 100,000 astronomical units — far beyond the heliopause — the Voyager probes cannot be considered entirely outside the solar system. (One astronomical unit, or AU, is the distance between the Earth and the sun — 93 million miles, or 150 million kilometres).

Oort cloud Image by TypePad, http://goo.gl/NWlQz6

Oort Cloud, The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA, Universe Today

When Voyager 1 and 2 crossed the heliopause, their still-working particle instruments unveiled the historical events. The heliosphere functions as a shield, keeping out many of the higher-energy particles created by the cosmic rays generated by other stars.

Magnetosphere of Earth, original bitmap from NASA. SVG rendering by Aaron Kaase

By tracking both the low-energy particles found inside the solar system and the high-energy particles from outside of it, the instruments could reveal a sudden surge of cosmic rays alerting scientists that the spacecraft had left the solar system.

The ever-changing nature of the heliosphere makes it impossible to tell when Pioneer 10 and 11 will enter interstellar space. It’s even possible that one of them may have already.

As per NASA’s e-book Beyond Earth: A Chronicle of Deep Space Exploration, from Nov. 5, 2017, Pioneer 10 was approximately 118.824 AUs from Earth, farther than any craft besides Voyager 1. H(?), Although Pioneer 11 and the Voyager twins were all heading in the direction of the sun’s apparent travel, Pioneer 10 is headed toward the trailing side. 2017 research showed that the tail of the heliosphere is around 220 AU from the sun. Since Pioneer 10 travels about 2.5 AU/year, it will take Pioneer until roughly 2057–40 years — to reach the changing boundary.

Pioneer 11 was thought to be approximately 97.6 AUs from Earth as of Nov. 5, 2017, according to the same e-book. Unlike its twin, the spacecraft is travelling in about the same direction as the Voyagers. Voyager 2 crossed into interstellar medium at approximately 120 AUs. Since Pioneer 11 is moving at 2.3 AU/year, it should reach interstellar space in about eight years, around 2027 — assuming the boundary doesn’t change, which it probably will.

On Jan. 1, 2019, New Horizons made its most recent flyby of a solar system object, and it was launched much later than the other four. During this flyby, New Horizons was 43 AU from the sun. The mission’s principal investigator, Alan Stern, told Space.com that the spacecraft was travelling approximately 3.1 AU each year, or 31 AU in ten years. In another two decades, the spacecraft has a good chance of reaching interstellar space. If New Horizons crossed at Voyager 2’s same border (it won’t, but just consider as a baseline), it would make the trip in just under 24 years, in 2043. But it’s possible the ISM line will move inward, allowing it to cross sooner.

Although there won’t be a direct confirmation of crossing the heliopause with the Pioneer spacecraft, it’s possible that New Horizons will still be working, and will give us a detailed study of interstellar space. The particle detectors that it holds are much more potent than the ones on Voyager, Stern said. Moreover, New Horizons holds a dust detector that would offer insight into the area beyond the heliosphere.

However, whether or not they will still be functioning remains to be seen. As per Stern, power is the limiting factor. New Horizons runs off of decaying plutonium dioxide. Presently, the spacecraft has enough power to work until the late 2030s, said Stern, and it is currently in good working order.

If in the unlikely event that the ever-changing heliosphere remains static Pioneer 11 will be the next to cross the heliopause in 2027, followed by New Horizons in 2043. Pioneer 10, the first of the five spacecraft to launch, will be the last to leave the heliosphere, in 2057. Once again, this assumes the extremely unrealistic chance that the heliopause remaining static for the next four decades.

See the full article here .

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About Medium

Medium is an online publishing platform developed by Evan Williams, and launched in August 2012. It is owned by A Medium Corporation. The platform is an example of social journalism, having a hybrid collection of amateur and professional people and publications, or exclusive blogs or publishers on Medium, and is regularly regarded as a blog host.

Williams developed Medium as a way to publish writings and documents longer than Twitter’s 140-character (now 280-character) maximum.

From JPL-Caltech: “NASA’s Voyager 2 Probe Enters Interstellar Space”

From JPL-Caltech

Dec. 10, 2018

Dwayne Brown
Headquarters, Washington
202-358-1726 / 301-286-6284
dwayne.c.brown@nasa.gov

Karen Fox
Headquarters, Washington
301-286-6284
karen.c.fox@nasa.gov

Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov

This illustration shows the position of NASA’s Voyager 1 and Voyager 2 probes, outside of the heliosphere, a protective bubble created by the Sun that extends well past the orbit of Pluto.

For the second time in history, a human-made object has reached the space between the stars. NASA’s Voyager 2 probe now has exited the heliosphere – the protective bubble of particles and magnetic fields created by the Sun.

NASA/Voyager 2

Members of NASA’s Voyager team will discuss the findings at a news conference at 11 a.m. EST (8 a.m. PST) today at the meeting of the American Geophysical Union (AGU) in Washington. The news conference will stream live on the agency’s website.

Comparing data from different instruments aboard the trailblazing spacecraft, mission scientists determined the probe crossed the outer edge of the heliosphere on Nov. 5. This boundary, called the heliopause, is where the tenuous, hot solar wind meets the cold, dense interstellar medium. Its twin, Voyager 1, crossed this boundary in 2012, but Voyager 2 carries a working instrument that will provide first-of-its-kind observations of the nature of this gateway into interstellar space.

NASA/Voyager 1

Voyager 2 now is slightly more than 11 billion miles (18 billion kilometers) from Earth. Mission operators still can communicate with Voyager 2 as it enters this new phase of its journey, but information – moving at the speed of light – takes about 16.5 hours to travel from the spacecraft to Earth. By comparison, light traveling from the Sun takes about eight minutes to reach Earth.

Artist’s concept of Voyager 2 with 9 facts listed around it. Image Credit: NASA

The most compelling evidence of Voyager 2’s exit from the heliosphere came from its onboard Plasma Science Experiment (PLS), an instrument that stopped working on Voyager 1 in 1980, long before that probe crossed the heliopause. Until recently, the space surrounding Voyager 2 was filled predominantly with plasma flowing out from our Sun. This outflow, called the solar wind, creates a bubble – the heliosphere – that envelopes the planets in our solar system. The PLS uses the electrical current of the plasma to detect the speed, density, temperature, pressure and flux of the solar wind. The PLS aboard Voyager 2 observed a steep decline in the speed of the solar wind particles on Nov. 5. Since that date, the plasma instrument has observed no solar wind flow in the environment around Voyager 2, which makes mission scientists confident the probe has left the heliosphere.

Animated gif showing the plasma data. Image Credit: NASA/JPL-Caltech

“Working on Voyager makes me feel like an explorer, because everything we’re seeing is new,” said John Richardson, principal investigator for the PLS instrument and a principal research scientist at the Massachusetts Institute of Technology in Cambridge. “Even though Voyager 1 crossed the heliopause in 2012, it did so at a different place and a different time, and without the PLS data. So we’re still seeing things that no one has seen before.”

In addition to the plasma data, Voyager’s science team members have seen evidence from three other onboard instruments – the cosmic ray subsystem, the low energy charged particle instrument and the magnetometer – that is consistent with the conclusion that Voyager 2 has crossed the heliopause. Voyager’s team members are eager to continue to study the data from these other onboard instruments to get a clearer picture of the environment through which Voyager 2 is traveling.

“There is still a lot to learn about the region of interstellar space immediately beyond the heliopause,” said Ed Stone, Voyager project scientist based at Caltech in Pasadena, California.

Together, the two Voyagers provide a detailed glimpse of how our heliosphere interacts with the constant interstellar wind flowing from beyond. Their observations complement data from NASA’s Interstellar Boundary Explorer (IBEX), a mission that is remotely sensing that boundary. NASA also is preparing an additional mission – the upcoming Interstellar Mapping and Acceleration Probe (IMAP), due to launch in 2024 – to capitalize on the Voyagers’ observations.

“Voyager has a very special place for us in our heliophysics fleet,” said Nicola Fox, director of the Heliophysics Division at NASA Headquarters. “Our studies start at the Sun and extend out to everything the solar wind touches. To have the Voyagers sending back information about the edge of the Sun’s influence gives us an unprecedented glimpse of truly uncharted territory.”

While the probes have left the heliosphere, Voyager 1 and Voyager 2 have not yet left the solar system, and won’t be leaving anytime soon. The boundary of the solar system is considered to be beyond the outer edge of the Oort Cloud, a collection of small objects that are still under the influence of the Sun’s gravity.

Oort Cloud NASA

The width of the Oort Cloud is not known precisely, but it is estimated to begin at about 1,000 astronomical units (AU) from the Sun and to extend to about 100,000 AU. One AU is the distance from the Sun to Earth. It will take about 300 years for Voyager 2 to reach the inner edge of the Oort Cloud and possibly 30,000 years to fly beyond it.

The Voyager probes are powered using heat from the decay of radioactive material, contained in a device called a radioisotope thermal generator (RTG). The power output of the RTGs diminishes by about four watts per year, which means that various parts of the Voyagers, including the cameras on both spacecraft, have been turned off over time to manage power.

“I think we’re all happy and relieved that the Voyager probes have both operated long enough to make it past this milestone,” said Suzanne Dodd, Voyager project manager at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “This is what we’ve all been waiting for. Now we’re looking forward to what we’ll be able to learn from having both probes outside the heliopause.”

Voyager 2 launched in 1977, 16 days before Voyager 1, and both have traveled well beyond their original destinations. The spacecraft were built to last five years and conduct close-up studies of Jupiter and Saturn. However, as the mission continued, additional flybys of the two outermost giant planets, Uranus and Neptune, proved possible. As the spacecraft flew across the solar system, remote-control reprogramming was used to endow the Voyagers with greater capabilities than they possessed when they left Earth. Their two-planet mission became a four-planet mission. Their five-year lifespans have stretched to 41 years, making Voyager 2 NASA’s longest running mission.

The Voyager story has impacted not only generations of current and future scientists and engineers, but also Earth’s culture, including film, art and music. Each spacecraft carries a Golden Record of Earth sounds, pictures and messages.

NASA Voyager Golden Record

Since the spacecraft could last billions of years, these circular time capsules could one day be the only traces of human civilization.

Voyager’s mission controllers communicate with the probes using NASA’s Deep Space Network (DSN), a global system for communicating with interplanetary spacecraft. The DSN consists of three clusters of antennas in Goldstone, California; Madrid, Spain; and Canberra, Australia.

NASA Deep Space Network dish, Goldstone, CA, USA

NASA Canberra, AU, Deep Space Network

NASA Deep Space Network Madrid Spain

The Voyager Interstellar Mission is a part of NASA’s Heliophysics System Observatory, sponsored by the Heliophysics Division of NASA’s Science Mission Directorate in Washington. JPL built and operates the twin Voyager spacecraft. NASA’s DSN, managed by JPL, is an international network of antennas that supports interplanetary spacecraft missions and radio and radar astronomy observations for the exploration of the solar system and the universe. The network also supports selected Earth-orbiting missions. The Commonwealth Scientific and Industrial Research Organisation, Australia’s national science agency, operates both the Canberra Deep Space Communication Complex, part of the DSN, and the Parkes Observatory, which NASA has been using to downlink data from Voyager 2 since Nov. 8.

For more information about the Voyager mission, visit:

https://www.nasa.gov/voyager

More information about NASA’s Heliophysics missions is available online at:

https://www.nasa.gov/sunearth

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Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge, on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

From Ethan Siegel: “Ask Ethan: What Happens When Stars Pass Through Our Solar System?”

Ethan Siegel
Apr 7, 2018

A recent study points to the possibility that just 70,000 years ago, a star passed through our Solar System. How often does this happen, and what are the consequences?

70,000 years ago, a brown dwarf pair known as Scholz’s Star, right on the precipice of igniting hydrogen fusion in its core, passed through the Solar System’s Oort cloud. Unlike the illustration, however, it still wouldn’t have been visible to human eyes. (José A. Peñas/SINC)

We like to think of our Solar System as a stable, mostly quiet place. Sure, we’ll find that the planets and other bodies in their orbits will kick around a comet or asteroid every once in a while, but for the most part, things are stable. Even the occasional interstellar visitor doesn’t pose much of a risk, at least, not to the integrity of worlds like our own. But our entire Solar System is orbiting through the galaxy, and that means it has hundreds of billions of chances to have a close interaction with another star. How often do we actually get one, and what are the potential consequences? That’s what our Patreon supporter Paweł Zuzelski wants to know (edited for English), as he asks:

How bad would it be if a star passed near the Sun? How close/large would it have to be to pose serious danger? How likely would such an event be?

The possibilities range from the mundane, where a few Oort cloud objects get thrown around, to the catastrophic, such as a collision with or ejection of an entire planet. Let’s take a look at what actually transpires.

Oort Cloud, The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA, Universe Today

Oort cloud Image by TypePad, http://goo.gl/NWlQz6

A map of star density in the Milky Way and surrounding sky, clearly showing the Milky Way, large and small Magellanic Clouds, and if you look more closely, NGC 104 to the left of the SMC, NGC 6205 slightly above and to the left of the galactic core, and NGC 7078 slightly below. All told, the Milky Way contains some 200 billion stars over its disk-like extent. (ESA/GAIA)

ESA/GAIA satellite

Our best estimates are that there are between 200 and 400 billion stars in our own Milky Way galaxy.

Milky Way Galaxy Credits: NASA/JPL-Caltech/R. Hurt

Although stars come in a huge variety of sizes and masses, the majority of stars (around 3 out of every 4) are red dwarf stars: somewhere between 8% and 40% the mass of our Sun. These stars have similarly smaller physical sizes than our Sun: on average, about 25% the Sun’s diameter. And finally, we know roughly how big the Milky Way is: a disk around 2,000 light years thick, around 100,000 light years across, and with a central bulge that’s around 5,000–8,000 light years in radius.

2cc73-reddwarfstar http://www.physics-astronomy.com/2014/06/red-dwarf-stars-may-answer-question-are.html#.Ws1h7YH3h_I

Finally, relative to the Sun, the typical star moves at a speed of around 20 km/s: about 1/10th of the speed that the Sun (and all the stars) orbit through the Milky Way itself.

These are the stats on the stars within our galaxy. There are plenty of details, caveats, and nuances that we are ignoring here, like the density changing with respect to whether we’re in a spiral arm or not, the fact that there are more stars towards the center than the outskirts (and our Sun is mid-way towards the edge), the inclination of the orbits in our Solar System with respect to the galaxy, and slight changes dependent on whether we’re in the center of the galactic plane or not. But the reason we can ignore them is that just from the above approximation, these numbers allow us to calculate how often stars from the galaxy come within a specific distance of our Sun, and therefore, how often we can expect a close encounter of various impacts.

The distances between the Sun and many of the nearest stars shown here are accurate, but each star — even the largest ones here — would be less than one-one millionth of a pixel in diameter if this were to scale. (Andrew Z. Colvin / Wikimedia Commons)

The way we compute it is very simple: we calculate the number density of stars, the cross-section we’re interested in (defined by how close you want another star to get to our own), and the speed with which the stars move relative to each other, and then multiply them all together to get the collision rate. This method of computation for a collision rate is useful for everything from particle physics to condensed matter physics (for the experts, this is basically the Drude model), and it applies just as readily to astrophysics. If we assume there are 200 billion stars in the Milky Way, that the stars are evenly distributed throughout the disk (and we ignore the bulge), and that 20 km/s is the speed that the stars move relative to one another, here’s what we get if we plot the interaction rate vs. the distance from the Sun.

A plot of how frequently a star within the Milky Way is likely to pass within a certain distance of our Sun. This is a log-log plot, with distance on the y-axis and how long you typically need to wait for such an event to happen on the x-axis. (E. Siegel)

It tells us that, on average, the closest we can expect a star to have come to the Sun over the history of the Universe is around 500 A.U., or about ten times the distance from the Sun to Pluto. It tells us that, once every billion years, we can expect a star to come within about 1,500 A.U. of the Sun, close to the edge of the scattered Kuiper belt. And more frequently, about once every 300,000 years or so, we’ll get a star that comes within about a light year of us.

A logarithmic view of our Solar System, extending out all the way to the next-nearest stars, shows the extend of the asteroid belt Kuiper belt, and Oort cloud. While stars passing through the Oort cloud may be common, they are exceedingly unlikely to have passed by any closer than that. (NASA)

Kuiper Belt. Minor Planet Center

Asteroid Belt NASA

This is good for the long-term stability of the planets in our Solar System, for certain. It tells us that over our Solar System’s 4.5 billion year history, the odds that a star would come as close to any of the planets as our Sun is to Pluto is approximately 1-in-10,000; the odds that a star would come as close to a planet as the Sun is to Earth (which would severely disrupt an orbit and cause an ejection) is less than 1-in-1,000,000,000. It means that the likelihood of another star in the galaxy passing by us and causing us severe difficulties is terrifically low. We cannot bet on us losing the cosmic lottery, and the odds are that we haven’t lost it so far, and won’t for the foreseeable future.

Orbits of the inner and outer planets, all obeying Kepler’s laws. The odds of a passing star coming within any appreciable distance of even Pluto are extremely low. (NASA / JPL-Caltech / R. Hurt, modified by E. Siegel)

But there have probably been upwards of 40,000 times that a star has passed through the Oort cloud (defined as 1.9 light years from the Sun), disrupting a large number of icy bodies in the process. Stars are interesting when they pass through the Solar System like this, because of the combination of two factors:

Oort cloud objects are very loosely bound to the Solar System, meaning that a very small gravitational tug is enough to alter their orbits significantly.
Stars are very massive, so a star that passes the same distance from an object as that object is from the Sun can “kick” it enough to alter its orbit.

This tells us that whenever we do experience a close encounter with a passing star, we’re at an increased risk, for perhaps the next few million years, of a collision with an incoming object from the Oort cloud.

In other words, the effects of a passing star won’t have an observable effect on what icy, comet-like bodies come into the inner Solar System until another 20 or so additional stars have had a close encounter with our own! This is problematic, because the last star system that passed near our own Sun, Scholz’s star (which did so 70,000 years ago), is already 20 light years away from us. However, there is a potentially optimistic thing that comes from this analysis: as we come to better map out and understand the stars and their motions within the nearest 500 light years, we can better predict when-and-where rogue, incoming Oort cloud objects are likely to arise. If we’re concerned with planetary defense from objects hurled inwards by passing stars, this kind of knowledge is the obvious next step.

WISEPC J045853.90+643451.9, shown in green, is the first ultra-cool brown dwarf discovered by NASA’s Wide-field Infrared Survey Explorer, or WISE.

NASA/WISE Telescope

This star is located about 20 light years away; to survey the entire sky and get the stars that may have passed within the Sun’s vicinity to cause potential Oort cloud storms today, we will have to go out to about 500 light years. (NASA/JPL-Caltech/UCLA)

It will require building wide-field surveying telescopes capable of seeing faint stars out to great distances. NASA’s Wide-field Infrared Survey Explorer (WISE) mission was the prototype for this, but the distances over which it could observe the faintest, most common stars was severely limited by its size and observing time. An all-sky, infrared space telescope could map the neighborhood around us out, telling us what’s likely to arrive, on what timescales, from what directions, and what star caused these perturbations in the Oort cloud objects. Gravitational interactions are always occurring, as even though there’s a great distance between stars in space, the Oort cloud is huge, and we literally have all the time in the world for objects to pass by and affect us. Given enough chances, everything you can imagine will occur.

See the full article here .

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“Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

From Universe today: “Where Do Comets Come From? Exploring the Oort Cloud”

Universe Today

19 Oct , 2017
Fraser Cain

Oort cloud Image by TypePad, http://goo.gl/NWlQz6

Oort Cloud NASA

Oort Cloud, The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA, Universe Today

Before I get into this article, I want to remind everyone that it’s been several decades since I’ve been able to enjoy a bright comet in the night sky. I’ve seen mind blowing auroras, witnessed a total solar eclipse with my own eyeballs, and seen a rocket launch. The Universe needs to deliver this bright comet for me, and it needs to do it soon.

By writing this article now, I will summon it. I will create an article that’ll be hilariously out of date in a few months, when that bright comet shows up.

Like that time we totally discovered a supernova in the Virtual Star Party, by saying there wasn’t a supernova in that galaxy, but there was, and we didn’t get to make the discovery.

Anyway, on to the article. Let’s talk about comets.

See the full article here .

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From Universe Today: “Now We Know When Stars Will Be Passing Through the Oort Cloud”

Universe Today

6 Sep , 2017
Matt Williams

To our Solar System, “close-encounters” with other stars happen regularly – the last occurring some 70,000 years ago and the next likely to take place 240,000 to 470,000 years from now. While this might sound like a “few and far between” kind of thing, it is quite regular in cosmological terms. Understanding when these encounters will happen is also important since they are known to cause disturbances in the Oort Cloud, sending comets towards Earth.

Thanks to a new study by Coryne Bailer-Jones, a researcher from the Max Planck Institute for Astronomy, astronomers now have refined estimates on when the next close-encounters will be happening. After consulting data from the ESA’s Gaia spacecraft, he concluded that over the course of the next 5 million years, that the Solar System can expect 16 close encounters, and one particularly close one!

ESA/GAIA satellite

For the sake of the study – which recently appeared in the journal Astronomy & Astrophysics under the titleThe Completeness-Corrected Rate of Stellar Encounters with the Sun From the First Gaia Data Release – Dr. Bailer Jones used Gaia data to track the movements of more than 300,000 stars in our galaxy to see if they would ever pass close enough to the Solar System to cause a disturbance.

See the full article here .

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From JPL: “Large, Distant Comets More Common Than Previously Thought”

JPL-Caltech

July 25, 2017
Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
elizabeth.landau@jpl.nasa.gov

This illustration shows how scientists used data from NASA’s WISE spacecraft to determine the nucleus sizes of comets. They subtracted a model of how dust and gas behave in comets in order to obtain the core size. Credit: NASA/JPL-Caltech.

An animation of a comet. Credit: NASA/JPL-Caltech.

Comets that take more than 200 years to make one revolution around the Sun are notoriously difficult to study. Because they spend most of their time far from our area of the solar system, many “long-period comets” will never approach the Sun in a person’s lifetime. In fact, those that travel inward from the Oort Cloud — a group of icy bodies beginning roughly 186 billion miles (300 billion kilometers) away from the Sun — can have periods of thousands or even millions of years.

Oort Cloud NASA

NASA’s WISE spacecraft, scanning the entire sky at infrared wavelengths, has delivered new insights about these distant wanderers.

NASA/WISE Telescope

Scientists found that there are about seven times more long-period comets measuring at least 0.6 miles (1 kilometer) across than had been predicted previously. They also found that long-period comets are on average up to twice as large as “Jupiter family comets,” whose orbits are shaped by Jupiter’s gravity and have periods of less than 20 years.

Researchers also observed that in eight months, three to five times as many long-period comets passed by the Sun than had been predicted. The findings are published in The Astronomical Journal.

“The number of comets speaks to the amount of material left over from the solar system’s formation,” said James Bauer, lead author of the study and now a research professor at the University of Maryland, College Park. “We now know that there are more relatively large chunks of ancient material coming from the Oort Cloud than we thought.”

The Oort Cloud is too distant to be seen by current telescopes, but is thought to be a spherical distribution of small icy bodies at the outermost edge of the solar system. The density of comets within it is low, so the odds of comets colliding within it are rare. Long-period comets that WISE observed probably got kicked out of the Oort Cloud millions of years ago. The observations were carried out during the spacecraft’s primary mission before it was renamed NEOWISE and reactivated to target near-Earth objects (NEOs).

“Our study is a rare look at objects perturbed out of the Oort Cloud,” said Amy Mainzer, study co-author based at NASA’s Jet Propulsion Laboratory, Pasadena, California, and principal investigator of the NEOWISE mission. “They are the most pristine examples of what the solar system was like when it formed.”

Astronomers already had broader estimates of how many long-period and Jupiter family comets are in our solar system, but had no good way of measuring the sizes of long-period comets. That is because a comet has a “coma,” a cloud of gas and dust that appears hazy in images and obscures the cometary nucleus. But by using the WISE data showing the infrared glow of this coma, scientists were able to “subtract” the coma from the overall comet and estimate the nucleus sizes of these comets. The data came from 2010 WISE observations of 95 Jupiter family comets and 56 long-period comets.

The results reinforce the idea that comets that pass by the Sun more often tend to be smaller than those spending much more time away from the Sun. That is because Jupiter family comets get more heat exposure, which causes volatile substances like water to sublimate and drag away other material from the comet’s surface as well.

“Our results mean there’s an evolutionary difference between Jupiter family and long-period comets,” Bauer said.

The existence of so many more long-period comets than predicted suggests that more of them have likely impacted planets, delivering icy materials from the outer reaches of the solar system.

Researchers also found clustering in the orbits of the long-period comets they studied, suggesting there could have been larger bodies that broke apart to form these groups.

The results will be important for assessing the likelihood of comets impacting our solar system’s planets, including Earth.

“Comets travel much faster than asteroids, and some of them are very big,” Mainzer said. “Studies like this will help us define what kind of hazard long-period comets may pose.”

NASA’s Jet Propulsion Laboratory in Pasadena, California, managed and operated WISE for NASA’s Science Mission Directorate in Washington. The NEOWISE project is funded by the Near Earth Object Observation Program, now part of NASA’s Planetary Defense Coordination Office. The spacecraft was put into hibernation mode in 2011 after twice scanned the entire sky, thereby completing its main objectives. In September 2013, WISE was reactivated, renamed NEOWISE and assigned a new mission to assist NASA’s efforts to identify potentially hazardous near-Earth objects.

For more information on WISE, visit:

https://www.nasa.gov/wise

See the full article here .

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Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

From Space.com- “Oort Cloud: The Outer Solar System’s Icy Shell” 2012

SPACE.com

July 02, 2012
Nola Taylor Redd

A giant shell of icy bodies known as the Oort Cloud encircles the solar system. When its inhabitants interact with passing stars, molecular clouds, and gravity from the galaxy, they may find themselves spiraling inward toward the sun, or cast completely out of the solar system into distant regions of space. Although this shell was first proposed in 1950, its extreme distance makes it challenging for scientists to identify objects within it.

Identifying the Oort Cloud

Within a few million years the light from bright stars will have boiled away this molecular cloud of gas and dust. The cloud has broken off from the Carina Nebula. Newly formed stars are visible nearby, their images reddened by blue light being preferentially scattered by the pervasive dust. This image spans about two light-years and was taken by the Hubble Space Telescope in 1999.

Hubble

Detail of Carina Nebula taken by the VLT telescope Credit: ESO

ESO/VLT

In 1950, Dutch astronomer Jan Oort suggested that some of the comets entering the solar system come from a cloud of icy bodies that may lie as far as 100,000 times Earth’s distance from the sun, a distance of up to 93 trillion miles (150 trillion kilometers).

Two types of comets travel through the solar system. Those with short periods, on the order of a few hundred years, stem from the Kuiper Belt, a pancake of icy particles near the orbit of Pluto. Longer period comets, with orbits of thousands of years, come from the more distant Oort Cloud.

Known objects in the Kuiper belt beyond the orbit of Neptune (scale in AU; epoch as of January 2015). Source: Minor Planet Center, http://www.cfeps.ne

The two regions vary primarily in terms of distance and location. The Kuiper Belt orbits in approximately the same plane as the planets, ranging from 30 to 50 times as far from the Sun as Earth. But the Oort Cloud is a shell that surrounds the entire solar system, and is a hundred times as distant.

Comets from the Oort Cloud can travel as far as three light-years from the sun. The farther they go, the weaker the sun’s gravitational hold grows. Passing stars and clouds of molecular gas can easily change the orbit of these comets, stripping them from our star or casting them back toward it. The path of the comets is constantly shifting, depending on what factors influence it.

Oort Cloud inhabitants

The estimated two trillion objects in the Oort Cloud are primarily composed of ices such as ammonia, methane, and water. Formed in the beginning of the solar system, they remain pristine chunks of its early life, allowing comets to provide insight into the environment in which the early Earth evolved. While gravity drew other bits of dust and ice together into larger celestial bodies, the residents of the Oort Cloud weren’t as fortunate. Gravity from the other planets—primarily gas giants such as Jupiter—kicked them into the outer solar system, where they remain.

The population of the Oort Cloud is in a constant state of flux. Not only are some of its residents permanently booted out of the system through interactions with passing neighbors, the sun may also capture the inhabitants from the shells surrounding other stars. Some of the bodies plunging toward the sun may have been kidnapped early in the sun’s evolution, when it was part of a more closely-packed cluster of stars.

When the comet Hyakutake passed within 9 million miles (15 million kilometers) of Earth in 1996, it was completing a journey of about 17,000 years from the distant reaches of the Oort Cloud. Hale-Bopp was another long-period comet that traveled in from the Oort Cloud. Visible for nearly a year and a half, it passed within 122 million miles (197 million kilometers) of the Earth. Both of these Oort Cloud objects had their orbits drastically changed as a result of their pass through the solar system. Halley’s Comet is also believed to have originally come from the Oort Cloud, although it is now a Kuiper Belt object.

Hyakutake

The comet Hale-Bopp captured the attention of millions when it traveled in from the Oort Cloud to pass near the Earth before returning to its distant home. Credit: J. C. Casado

Scientists have identified four other objects that they believe are part of this distant group. The largest of the four, Sedna, thought to be three-quarters the size of Pluto, lies 8 billion miles (13 billion kilometers) from Earth and orbits the sun approximately every 10,500 years. The other three objects are known as 2006 SQ372, 2008 KV42, and 2000 CR105, and range between 30 to 155 miles (50 to 250 km) in size.

See the full article here.

Please help promote STEM in your local schools.

Stem Education Coalition

From SPACE.com: “Oort Cloud: The Outer Solar System’s Icy Shell” 2012

SPACE.com

July 02, 2012
Nola Taylor Redd

A giant shell of icy bodies known as the Oort Cloud encircles the solar system. When its inhabitants interact with passing stars, molecular clouds, and gravity from the galaxy, they may find themselves spiraling inward toward the sun, or cast completely out of the solar system into distant regions of space. Although this shell was first proposed in 1950, its extreme distance makes it challenging for scientists to identify objects within it.

Artists rendering of the Kuiper Belt and Oort Cloud. Credit: NASA

Identifying the Oort Cloud

In 1950, Dutch astronomer Jan Oort suggested that some of the comets entering the solar system come from a cloud of icy bodies that may lie as far as 100,000 times Earth’s distance from the sun, a distance of up to 93 trillion miles (150 trillion kilometers).

Two types of comets travel through the solar system. Those with short periods, on the order of a few hundred years, stem from the Kuiper Belt, a pancake of icy particles near the orbit of Pluto. Longer period comets, with orbits of thousands of years, come from the more distant Oort Cloud.

Kuiper Belt

The two regions vary primarily in terms of distance and location. The Kuiper Belt orbits in approximately the same plane as the planets, ranging from 30 to 50 times as far from the Sun as Earth. But the Oort Cloud is a shell that surrounds the entire solar system, and is a hundred times as distant.

Comets from the Oort Cloud can travel as far as three light-years from the sun. The farther they go, the weaker the sun’s gravitational hold grows. Passing stars and clouds of molecular gas can easily change the orbit of these comets, stripping them from our star or casting them back toward it. The path of the comets is constantly shifting, depending on what factors influence it.

Oort Cloud inhabitants

The estimated two trillion objects in the Oort Cloud are primarily composed of ices such as ammonia, methane, and water. Formed in the beginning of the solar system, they remain pristine chunks of its early life, allowing comets to provide insight into the environment in which the early Earth evolved. While gravity drew other bits of dust and ice together into larger celestial bodies, the residents of the Oort Cloud weren’t as fortunate. Gravity from the other planets—primarily gas giants such as Jupiter—kicked them into the outer solar system, where they remain.

The population of the Oort Cloud is in a constant state of flux. Not only are some of its residents permanently booted out of the system through interactions with passing neighbors, the sun may also capture the inhabitants from the shells surrounding other stars. Some of the bodies plunging toward the sun may have been kidnapped early in the sun’s evolution, when it was part of a more closely-packed cluster of stars.

The comet Hale-Bopp captured the attention of millions when it traveled in from the Oort Cloud to pass near the Earth before returning to its distant home.
Credit: J. C. Casado

When the comet Hyakutake passed within 9 million miles (15 million kilometers) of Earth in 1996, it was completing a journey of about 17,000 years from the distant reaches of the Oort Cloud. Hale-Bopp was another long-period comet that traveled in from the Oort Cloud. Visible for nearly a year and a half, it passed within 122 million miles (197 million kilometers) of the Earth. Both of these Oort Cloud objects had their orbits drastically changed as a result of their pass through the solar system. Halley’s Comet is also believed to have originally come from the Oort Cloud, although it is now a Kuiper Belt object.

Halley’s Comet on 8 March 1986

Scientists have identified four other objects that they believe are part of this distant group. The largest of the four, Sedna, thought to be three-quarters the size of Pluto, lies 8 billion miles (13 billion kilometers) from Earth and orbits the sun approximately every 10,500 years. The other three objects are known as 2006 SQ372, 2008 KV42, and 2000 CR105, and range between 30 to 155 miles (50 to 250 km) in size.

See the full article here.

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