NASA's TESS Mission finds its smallest planet so far

NASA's Transient Exoplanet Exploration Satellite (TESS) has discovered a world between the sizes of Mars and Earth in orbit around a bright, cold, nearby star. The planet, called L 98-59b, marks the smallest discovered by TESS to date.
Two other worlds orbit the same star. While the sizes of the three planets are known, additional studies with other telescopes will be needed to determine if they have atmospheres and, if so, what gases are present. Worlds L 98-59 almost double the number of small exoplanets, that is, planets beyond our solar system, that have the best potential for this type of tracking.
"The discovery is a great scientific and engineering achievement for TESS," said Veselin Kostov, an Astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and the SETI Institute in Mountain View, California. "For atmospheric studies of small planets, short orbits are needed around bright stars, but such planets are difficult to detect, and this system has the potential for fascinating future studies."
An article on the findings, directed by Kostov, was published in the June 27 issue of The Astronomical Journal.
L 98-59b is approximately 80% the size of the Earth and 10% smaller than the previous record holder discovered by TESS. Its host star, L 98-59, is an M dwarf of about one third of the Sun's mass and is about 35 light-years away in the southern constellation of Volans. Although L 98-59b is a record for TESS, even smaller planets have been discovered in data collected by NASA's Kepler satellite, including Kepler-37b, which is only 20% larger than the Moon.
The other two worlds in the system, L 98-59c and L 98-59d, are respectively around 1.4 and 1.6 times the size of the Earth. The three were discovered by TESS using transits, and the periodic drops in the brightness of the star caused when each planet passes in front of it.
TESS monitors a region of the sky of 24 by 96 degrees, called sector, for 27 days at a time. When the satellite finishes its first year of observations in July, the L 98-59 system will have appeared in seven of the 13 sectors that make up the southern sky. Kostov's team hopes that this will allow scientists to refine what is known about the three confirmed planets and look for additional worlds.
"If you have more than one planet in orbit in a system, they can interact gravitationally with each other," said Jonathan Brande, co-author and astrophysicist at Goddard and the University of Maryland, College Park. "TESS will observe L 98-59 in enough sectors to be able to detect planets with orbits around 100 days, but if we are very lucky, we could see the gravitational effects of undiscovered planets in which we are currently aware."
M dwarfs like L 98-59 represent three-quarters of the star population of our Milky Way galaxy. But they are no larger than about half the mass of the Sun and are much colder, with surface temperatures of less than 70% that of the Sun. Other examples include TRAPPIST-1, which houses a system of seven planets of the Sun. size of the Earth, and Proxima Centauri, our nearest star neighbor, which has a confirmed planet. Because these small, cold stars are so common, scientists want to learn more about the planetary systems that form around them.
L 98-59b, the innermost world, orbits every 2.25 days, staying so close to the star that it receives up to 22 times the amount of energy that the Earth receives from the Sun. The average planet, L 98-59c, orbits every 3.7 days and experiences approximately 11 times more radiation than Earth. L 98-59d, the farthest planet identified so far in the system, orbits every 7.5 days and has an explosion of about four times the radiant energy of the Earth.
None of the planets is within the "habitable zone" of the star, the range of distances from the star where liquid water could exist on its surfaces. However, they all occupy what scientists call the Venus zone, a range of stellar distances where a planet with an initial atmosphere similar to Earth could experience a runaway greenhouse effect that transforms it into an atmosphere similar to that of Venus. Based on its size, the third planet could be a rocky world similar to Venus or one more like Neptune, with a small rocky core wrapped in a deep atmosphere.
By: Preeti Narula
Content: https://www.sciencedaily.com/releases/2019/06/190627114113.htm