From UCSC: “Pluto’s hydrocarbon haze keeps dwarf planet colder than expected”

UC Santa Cruz

UC Santa Cruz

November 15, 2017
Tim Stephens
stephens@ucsc.edu

New analysis of Pluto’s atmosphere explains why New Horizons spacecraft measured temperatures much colder than predicted.

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Pluto’s haze layer is blue in this image taken by the New Horizons Ralph/Multispectral Visible Imaging Camera and computer generated to replicate true color. Haze is produced by sunlight-initiated chemical reactions of nitrogen and methane, leading to small particles that grow and settle toward the surface. (Image credit: NASA/JHUAPL/SwRI)

NASA/New Horizons spacecraft

The gas composition of a planet’s atmosphere generally determines how much heat gets trapped in the atmosphere. For the dwarf planet Pluto, however, the predicted temperature based on the composition of its atmosphere was much higher than actual measurements taken by NASA’s New Horizons spacecraft in 2015.

A new study published November 16 in Nature proposes a novel cooling mechanism controlled by haze particles to account for Pluto’s frigid atmosphere.

“It’s been a mystery since we first got the temperature data from New Horizons,” said first author Xi Zhang, assistant professor of Earth and planetary sciences at UC Santa Cruz. “Pluto is the first planetary body we know of where the atmospheric energy budget is dominated by solid-phase haze particles instead of by gases.”

The cooling mechanism involves the absorption of heat by the haze particles, which then emit infrared radiation, cooling the atmosphere by radiating energy into space. The result is an atmospheric temperature of about 70 Kelvin (minus 203 degrees Celsius, or minus 333 degrees Fahrenheit), instead of the predicted 100 Kelvin (minus 173 Celsius, or minus 280 degrees Fahrenheit).

According to Zhang, the excess infrared radiation from haze particles in Pluto’s atmosphere should be detectable by the James Webb Space Telescope, allowing confirmation of his team’s hypothesis after the telescope’s planned launch in 2019.

NASA/ESA/CSA Webb Telescope annotated

Extensive layers of atmospheric haze can be seen in images of Pluto taken by New Horizons. The haze results from chemical reactions in the upper atmosphere, where ultraviolet radiation from the sun ionizes nitrogen and methane, which react to form tiny hydrocarbon particles tens of nanometers in diameter. As these tiny particles sink down through the atmosphere, they stick together to form aggregates that grow larger as they descend, eventually settling onto the surface.

“We believe these hydrocarbon particles are related to the reddish and brownish stuff seen in images of Pluto’s surface,” Zhang said.

The researchers are interested in studying the effects of haze particles on the atmospheric energy balance of other planetary bodies, such as Neptune’s moon Triton and Saturn’s moon Titan. Their findings may also be relevant to investigations of exoplanets with hazy atmospheres.

Zhang’s coauthors are Darrell Strobel, a planetary scientist at Johns Hopkins University and co-investigator on the New Horizons mission, and Hiroshi Imanaka, a scientist at NASA Ames Research Center in Mountain View, who studies the chemistry of haze particles in planetary atmospheres. This research was funded by NASA.

See the full article here .

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UCO Lick Shane Telescope
UCO Lick Shane Telescope interior
Shane Telescope at UCO Lick Observatory, UCSC

Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

UC Santa Cruz campus
The University of California, Santa Cruz, opened in 1965 and grew, one college at a time, to its current (2008-09) enrollment of more than 16,000 students. Undergraduates pursue more than 60 majors supervised by divisional deans of humanities, physical & biological sciences, social sciences, and arts. Graduate students work toward graduate certificates, master’s degrees, or doctoral degrees in more than 30 academic fields under the supervision of the divisional and graduate deans. The dean of the Jack Baskin School of Engineering oversees the campus’s undergraduate and graduate engineering programs.

UCSC is the home base for the Lick Observatory.

Lick Observatory's Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building
Lick Observatory’s Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building

Search for extraterrestrial intelligence expands at Lick Observatory
New instrument scans the sky for pulses of infrared light
March 23, 2015
By Hilary Lebow
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The NIROSETI instrument saw first light on the Nickel 1-meter Telescope at Lick Observatory on March 15, 2015. (Photo by Laurie Hatch) UCSC Lick Nickel telescope

Astronomers are expanding the search for extraterrestrial intelligence into a new realm with detectors tuned to infrared light at UC’s Lick Observatory. A new instrument, called NIROSETI, will soon scour the sky for messages from other worlds.

“Infrared light would be an excellent means of interstellar communication,” said Shelley Wright, an assistant professor of physics at UC San Diego who led the development of the new instrument while at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics.

Wright worked on an earlier SETI project at Lick Observatory as a UC Santa Cruz undergraduate, when she built an optical instrument designed by UC Berkeley researchers. The infrared project takes advantage of new technology not available for that first optical search.

Infrared light would be a good way for extraterrestrials to get our attention here on Earth, since pulses from a powerful infrared laser could outshine a star, if only for a billionth of a second. Interstellar gas and dust is almost transparent to near infrared, so these signals can be seen from great distances. It also takes less energy to send information using infrared signals than with visible light.

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UCSC alumna Shelley Wright, now an assistant professor of physics at UC San Diego, discusses the dichroic filter of the NIROSETI instrument. (Photo by Laurie Hatch)

Frank Drake, professor emeritus of astronomy and astrophysics at UC Santa Cruz and director emeritus of the SETI Institute, said there are several additional advantages to a search in the infrared realm.

“The signals are so strong that we only need a small telescope to receive them. Smaller telescopes can offer more observational time, and that is good because we need to search many stars for a chance of success,” said Drake.

The only downside is that extraterrestrials would need to be transmitting their signals in our direction, Drake said, though he sees this as a positive side to that limitation. “If we get a signal from someone who’s aiming for us, it could mean there’s altruism in the universe. I like that idea. If they want to be friendly, that’s who we will find.”

Scientists have searched the skies for radio signals for more than 50 years and expanded their search into the optical realm more than a decade ago. The idea of searching in the infrared is not a new one, but instruments capable of capturing pulses of infrared light only recently became available.

“We had to wait,” Wright said. “I spent eight years waiting and watching as new technology emerged.”

Now that technology has caught up, the search will extend to stars thousands of light years away, rather than just hundreds. NIROSETI, or Near-Infrared Optical Search for Extraterrestrial Intelligence, could also uncover new information about the physical universe.

“This is the first time Earthlings have looked at the universe at infrared wavelengths with nanosecond time scales,” said Dan Werthimer, UC Berkeley SETI Project Director. “The instrument could discover new astrophysical phenomena, or perhaps answer the question of whether we are alone.”

NIROSETI will also gather more information than previous optical detectors by recording levels of light over time so that patterns can be analyzed for potential signs of other civilizations.

“Searching for intelligent life in the universe is both thrilling and somewhat unorthodox,” said Claire Max, director of UC Observatories and professor of astronomy and astrophysics at UC Santa Cruz. “Lick Observatory has already been the site of several previous SETI searches, so this is a very exciting addition to the current research taking place.”

NIROSETI will be fully operational by early summer and will scan the skies several times a week on the Nickel 1-meter telescope at Lick Observatory, located on Mt. Hamilton east of San Jose.

The NIROSETI team also includes Geoffrey Marcy and Andrew Siemion from UC Berkeley; Patrick Dorval, a Dunlap undergraduate, and Elliot Meyer, a Dunlap graduate student; and Richard Treffers of Starman Systems. Funding for the project comes from the generous support of Bill and Susan Bloomfield.

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