Since NASA’s Kepler Space Telescope was launched in 2009, the study of extrasolar planets has seen an explosion. With Kepler’s resignation in 2018, missions like the Transiting Exoplanet Survey Satellite (TESS) fell victim to picking up where its predecessor left off. Using observations from TESS, an international team of astronomers recently discovered three exoplanets orbiting a young sun-like star named TOI 451.
The research was led by Elisabeth R. Newton, an assistant professor of physics and astronomy at Dartmouth College. It was joined by researchers from NASA JPL, NASA Goddard, NASA Ames, the NASA Exoplanet Science Institute, the SETI Institute, the Max Planck Institute for Astronomy, the Kavli Institute for Astrophysics and Space Research as well as several universities and observatories .
Using data from TESS, the team examined stars in the Pisces-Eridanus Current, a collection of stars located ~ 260 to 737 light years from Earth. This stream is approximately 1,300 light years long, spans 14 constellations, and is named for those that contain the highest concentrations. This stream was discovered in 2019 by a team led by Stefan Meingast using data obtained from ESA’s Gaia mission.
Yellow dots show the positions of known or suspected systems (with TOI 451 circled) that belong to the Pisces-Eridanus Current. Photo credit: NASA’s Goddard Space Flight Center
Later that year, researchers led by Jason Curtis – an astronomer and a fellow of the National Science Foundation (NSF) at Columbia University (and co-author of the study) – analyzed TESS data for several of these stars. What they found was that they had fast spin rates and prominent star spots (which led to periodic drops in luminosity), an indication that they are significantly younger than previously thought.
Based on these results, Curtis and colleagues found that the stream was only 120 million years old (3% as old as our sun). When Newton and her colleagues examined data that TESS had collected in the same stream between October and December 2018, they found that there were three exoplanets, particularly around one star. Known as TOI 451 (also known as CD-38 1467), this star is located about 400 light years away in the constellation Eridanus.
TOI 451 is a type G (yellow dwarf) star, which is about 88% the size of our sun, 95% as massive and also a little cooler and darker (as a young star). Another indication of its youth is the fact that it rotates once every 5.1 days – or five times faster than the sun. After the transits discovered by TESS, all three planets orbit TOI 451 closer than Mercury to our sun, making them all hot and inhospitable to life (as we know it).
Follow-up observations were made in 2019 and 2020 with NASA’s Spitzer Space Telescope (which retired January 30, 2020) and archival data collected by NASA’s near-earth wide-field infrared surveyor (NEOWISE) between 2009 and 2011 (which) had received at that time was still wise). Additional observations were made by the global network of the Las Cumbres Observatory and the Perth Exoplanet Survey Telescope in Australia.
An artist rendering of the Transiting Exoplanet Survey Satellite (TESS). Photo credit: NASA’s Goddard Space Flight Center
All of this confirmed the presence of these three exoplanets that fit the term “hot super-earth”. The WISE data also showed that TOI 451 is unusually bright in infrared light at wavelengths of 12 and 24 micrometers. This suggests the presence of a debris disk that the team estimates is about as far from the star as Jupiter is from our sun.
The team also examined a faint neighbor star that appeared to be in close proximity to TOI 451 in the TESS images. Using data from ESA’s Gaia Observatory, Newton’s team determined that this star is actually a binary system of two M-stars (red dwarf) that is a gravitational companion of TOI 451. As Prof. Newton recently stated in a NASA press publication:
“This system checks a lot of boxes for astronomers. It is only 120 million years old and only 400 light-years away, which allows detailed observations of this young planetary system. And because there are three planets that are two to four times the size of Earth, they are particularly promising targets for testing theories about how the planet’s atmosphere evolved. “
The innermost of these planets (TOI 451 b) is about 1.9 times as large as the earth, 2 to 12 times as large as the mass and has an orbital period of 1.9 days. TOI 451 c is about three times the size of the earth, 16 times as massive and has an orbital period of 9.2 days. The outermost planet (TOI 451 d) is four times the size of the earth, four to 19 times as massive and has an orbital period of 16 days. The temperature estimates range from about 1,200 ° C (2,200 ° F) for b to about 450 ° C (840 ° F) for d.
TOI 1338 b is a circumbinary planet orbiting its two stars. It was discovered by TESS. Photo credit: NASA’s Goddard Space Flight Center / Chris Smith
These results, along with its relative proximity to Earth, suggest that TOI 451 and other stars in the Pisces-Eridanus Current are likely excellent candidates for study. The young age of these stars in particular means that they can reveal a lot about the formation and development of stars and planets. Jessie Christiansen, co-author of the paper and assistant scientific director of the NASA Exoplanet Archive, stated:
“Thanks to TESS’s almost complete sky coverage, we already had measurements that could aid a search for planets orbiting members of this stream when the stream was identified. With TESS data, we can continue to expand the limits of our knowledge of exoplanets and their systems in the years to come. “
Like its predecessor, TESS searches for exoplanets by examining thousands of stars in a field and looking for periodic drops in brightness. These are indications of transits in which planets pass in front of the face of a star (relative to the observer). Under the right conditions, light falling through an exoplanet’s atmosphere can provide astronomers with spectra that can be used to determine the composition of an atmosphere.
Given their mass, astronomers expect the TOI 451 planets, despite their intense heat, to retain much of their atmosphere as they evolve. This means that future observations with next-generation telescopes could shed light on what those atmospheres are made of, and provide important clues as to how the atmospheres evolve over time.
Artist’s impression of the rocky super-earth HD 85512 b. Photo credit: ESO / M. Kornmesser
Elisa Quintana, astrophysicist at NASA’s Goddard Space Flight Center, said:
“By measuring the starlight that penetrates a planet’s atmosphere at different wavelengths, we can infer its chemical composition and the presence of clouds or cloudiness at high altitudes. TOI 451’s planets provide excellent targets for such studies with Hubble and the upcoming James Webb Space Telescope. “
At the time of this writing, a total of 4,352 exoplanets have been confirmed in 3,221 systems while another 5,765 candidates are awaiting confirmation. Many of these planets orbit stars similar to our own and not a few are considered “potentially habitable”. These are seen as good candidates for follow-up observations once the James Webb and Nancy Grace Roman space telescopes go into space.
While the planets from TOI 451 are likely to be uninhabitable, subsequent observations likely tell us a lot about how planets evolve, which could help us narrow down the search.
Further reading: NASA, The Astrophysical Journal