From University of Illinois at Urbana–Champaign (US) : “Earthlike planets in other solar systems? Look for moons”

From University of Illinois at Urbana–Champaign (US)

9/8/2021
Debra Levey Larson

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In this map of overlapping orbital resonances, the regions between resonances are colored black and could allow for stable satellite orbits under optimal conditions. The light green curve connects the first point of intersection between adjacent resonances and marks a stability boundary within the “three body problem”.

Finding an exact copy of the Earth somewhere in the universe sounds like a far-fetched notion, but scientists believe that because Earth happened in our solar system, something similar is bound to exist someplace else. University of Illinois Urbana-Champaign researcher Siegfried Eggl and his colleagues say orbiting moons may play a key role in keeping planets habitable over long periods and identified a method to find them.

“In our solar system, we have an average of 20 moons orbiting around each planet. So, we suspected there are moons around planets in other systems, too. There is really no reason why there shouldn’t be any,” said Eggl, a professor in the Department of Aerospace Engineering at UIUC.

Eggl said astronomers using the Atacama Large Millimeter Array have recently observed what they believe is evidence of a moon forming around the extrasolar planet PDS 70c.

The next step is finding moons around planets that have two stars.

Some planets in other solar systems can be seen using very large telescopes like ALMA, the W.M. Keck observatory in Hawaii, or the European Southern Observatory’s VLT in Chile, but fully formed moons are still too tiny to spot.

“We know they are there. We just need to look harder. But because it is so difficult to see them, we identified a way to detect them through the effect they have on a planet using transit timing variations.”

Eggl said they can observe how planets behave in orbit and compare those observations to models with and without moons.

“We know the planets, stars, and moons in our solar system interact gravitationally like a giant board game,” Eggl said. “The moon is tidally interacting with the Earth and slowing its own rotation, but the Sun is also there, tugging on both. A second star would act as another external perturber to the system.”

When a planet passes in front of a star the star dims a little, Eggl said. A moon tugging on the planet is causing the planet to wobble slightly on its orbit. This wobble makes the darkening of the star occur sometimes earlier and other times later. In a double star system, additional variations in the time of transit are due to the forced, elliptical orbits of the planet and its moon. If detected, those variations can lead to additional insights into the properties of the system.

Much like proving there is wind by observing tree branches bending, Eggl said “This is an indirect proof of a moon because there’s nothing else that could tug on the planet in that kind of fashion.”

Of course, this assumes that planets did not lose their moons along the way.

“We first had to determine the orbital resonances in the systems we looked at,” Eggl said. “When moons and planets have slightly elliptical orbits, they don’t always move at the same speed. The more eccentric an orbit, the more frequencies can be excited, and we see these resonances become more and more important. At some point there will be overlapping resonances that can lead to chaos in the system. In our study we have shown, however, that there is enough stable ‘real estate’ to merit a thorough search for moons around planets in double star systems.”

Billy Quarles, lead author of the study, said, “The major difference with binary systems is the companion star acts like the tide at the beach, where it periodically comes in and etches away the beachfront. With a more eccentric binary orbit, a larger portion of the stable ‘real estate’ is removed. This can help out a lot in our search for moons in other star systems.”

The bottom line for Eggl is that our solar system is probably not as special as we’d like to think it is.

“If we can use this method to show there are other moons out there, then there are probably other systems similar to ours,” he said. “The moon is also likely critical for the evolution of life on our planet, because without the moon the axis tilt of the Earth wouldn’t be as stable, the results of which would be detrimental to climate stability. Other peer-reviewed studies have shown the relationship between moons and the possibility of complex life.”

The study appears in The Astronomical Journal.

See the full article here .

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The University of Illinois at Urbana-Champaign (US) community of students, scholars, and alumni is changing the world.
The University of Illinois at Urbana–Champaign is a public land-grant research university in Illinois in the twin cities of Champaign and Urbana. It is the flagship institution of the University of Illinois system and was founded in 1867.
The University of Illinois at Urbana–Champaign is a member of the Association of American Universities (US) and is classified among “R1: Doctoral Universities – Very high research activity”, and has been listed as a “Public Ivy” in The Public Ivies: America’s Flagship Public Universities (2001) by Howard and Matthew Greene. In fiscal year 2019, research expenditures at Illinois totaled $652 million. The campus library system possesses the second-largest university library in the United States by holdings after Harvard University (US). The university also hosts the National Center for Supercomputing Applications (US) (NCSA).

The university contains 16 schools and colleges and offers more than 150 undergraduate and over 100 graduate programs of study. The university holds 651 buildings on 6,370 acres (2,578 ha). The University of Illinois at Urbana–Champaign also operates a Research Park home to innovation centers for over 90 start-up companies and multinational corporations, including Abbott, AbbVie, Caterpillar, Capital One, Dow, State Farm, and Yahoo, among others.

As of August 2020, the alumni, faculty members, or researchers of the university include 30 Nobel laureates; 27 Pulitzer Prize winners; 2 Turing Award winners and 1 Fields medalist. Illinois athletic teams compete in Division I of the NCAA and are collectively known as the Fighting Illini. They are members of the Big Ten Conference and have won the second-most conference titles. Illinois Fighting Illini football won the Rose Bowl Game in 1947, 1952, 1964 and a total of five national championships. Illinois athletes have won 29 medals in Olympic events, ranking it among the top 40 American universities with Olympic medals.

Illinois Industrial University

The original University Hall, which stood until 1938, when it was replaced by Gregory Hall and the Illini Union. Pieces were used in the erection of Hallene Gateway dedicated in 1998.

The University of Illinois, originally named “Illinois Industrial University”, was one of the 37 universities created under the first Morrill Land-Grant Act, which provided public land for the creation of agricultural and industrial colleges and universities across the United States. Among several cities, Urbana was selected in 1867 as the site for the new school. From the beginning, President John Milton Gregory’s desire to establish an institution firmly grounded in the liberal arts tradition was at odds with many state residents and lawmakers who wanted the university to offer classes based solely around “industrial education”. The university opened for classes on March 2, 1868 and had two faculty members and 77 students.

The Library which opened with the school in 1868 started with 1,039 volumes. Subsequently President Edmund J. James in a speech to the board of trustees in 1912 proposed to create a research library. It is now one of the world’s largest public academic collections. In 1870 the Mumford House was constructed as a model farmhouse for the school’s experimental farm. The Mumford House remains the oldest structure on campus. The original University Hall (1871) was the fourth building built. It stood where the Illini Union stands today.

University of Illinois

In 1885, the Illinois Industrial University officially changed its name to the “University of Illinois”, reflecting its agricultural; mechanical; and liberal arts curriculum.

During his presidency Edmund J. James (1904–1920) is credited for building the foundation for the large Chinese international student population on campus. James established ties with China through the Chinese Minister to the United States Wu Ting-Fang. In addition during James’s presidency class rivalries and Bob Zuppke’s winning football teams contributed to campus morale.
Like many universities the economic depression slowed construction and expansion on the campus. The university replaced the original university hall with Gregory Hall and the Illini Union. After World War II the university experienced rapid growth. The enrollment doubled and the academic standing improved. This period was also marked by large growth in the Graduate College and increased federal support of scientific and technological research. During the 1950s and 1960s the university experienced the turmoil common on many American campuses. Among these were the water fights of the fifties and sixties.

University of Illinois at Urbana–Champaign

By 1967 the University of Illinois system consisted of a main campus in Champaign-Urbana and two Chicago campuses- Chicago Circle (UICC) and Medical Center (UIMC). People began using “Urbana–Champaign” or the reverse to refer to the main campus specifically. The university name officially changed to the “University of Illinois at Urbana–Champaign” around 1982. While this was a reversal of the commonly used designation for the metropolitan area- “Champaign-Urbana” – most of the campus is located in Urbana. The name change established a separate identity for the main campus within the University of Illinois system which today includes campuses in Springfield (UIS) and Chicago (UIC) (formed by the merger of UICC and UIMC).

In 1998 the Hallene Gateway Plaza was dedicated. The Plaza features the original sandstone portal of University Hall which was originally the fourth building on campus. In recent years state support has declined from 4.5% of the state’s tax appropriations in 1980 to 2.28% in 2011- a nearly 50% decline. As a result the university’s budget has shifted away from relying on state support with nearly 84% of the budget now coming from other sources.

On March 12, 2015, the Board of Trustees approved the creation of a medical school, the first college created at Urbana–Champaign in 60 years. The Carle-Illinois College of Medicine began classes in 2018.

Research

The University of Illinois at Urbana–Champaign is often regarded as a world-leading magnet for engineering and sciences (both applied and basic). Having been classified into the category comprehensive doctoral with medical/veterinary and very high research activity by The Carnegie Foundation for the Advancement of Teaching Illinois offers a wide range of disciplines in undergraduate and postgraduate programs.

According to the National Science Foundation (US) the university spent $625 million on research and development in 2018 ranking it 37th in the nation. It is also listed as one of the Top 25 American Research Universities by The Center for Measuring University Performance. Beside annual influx of grants and sponsored projects the university manages an extensive modern research infrastructure. The university has been a leader in computer based education and hosted the PLATO project which was a precursor to the internet and resulted in the development of the plasma display. Illinois was a 2nd-generation ARPAnet site in 1971 and was the first institution to license the UNIX operating system from Bell Labs.