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Planet-Hunting TESS discovers its smallest exoplanet to date

Thanks to largely Kepler Space Telescope the number of confirmed extrasolar planets has grown exponentially over the last decade. And with next-generation missions like Transiting Exoplanet Survey Satellite (TESS) already in orbit, more candidates are being discovered and confirmed planets all the time – many of them are also new and exciting!

In fact, one of TESS's latest discoveries contains a three-plane system that orbits a star (L 98-59), which lies about 35 light-years from Earth. One of the planets, known as L 98-59b, is between the sizes of Earth and Mars – making it the smallest exoplanet discovered by TESS to date. The discovery also highlights the sophisticated TESS and doubles the number of small exoplanets considered worthy of follow-up studies.

The paper describing the discovery appeared in the latest issue of The Astrophysical Journal . The international team behind the discovery included several NASA researchers as well as researchers from the Harvard-Smithsonian Center for Astrophysics, the Kavli Institute for Astrophysics and Space Research, and several universities and observatories from around the world.

Veselin Kostov, an astrophysicist at NASA's Goddard Space Flight Center and the SETI Institute, was the lead author of the discovery paper. As he explained in a new NASA press release:

"The discovery is a great technical and scientific accomplishment for TESS. For atmospheric studies of small planets, you need short paths around bright stars, but such planets are difficult to detect. system has the potential for fascinating future studies. "

As the name confirms, TESS chases for exoplanets using the method known as Transit Photometry (also Transit Method). This involves observing distant stars for sudden dips in illumination, indicating that a planet passes in front of the star (ie, transiting) relative to the observer. By observing the magnitude and frequency of the dips, researchers can determine the existence of planets as well as their circulatory period and size.

While this method is currently the most effective way to detect and confirm exoplanets, which accounts for 3087 of the over 4,000 discovered so far. But it is not very effective when it comes to spotting smaller rocky planets like Earth. The fact that TESS could not find one, but three rocky planets orbiting L 98-59, is a testament to the sensitivity and ability of its instruments.

The three planets discovered in the L98-59 system at NASA's Transiting Exoplanet Survey Satellite are compared to Mars and Earth in order of increasing size in this illustration. Credit: NASA's Goddard Space Flight Center

These planets (designated L 98-59b, c and d) are about 0.8, 1.4, and 1.6 times the size of the earth and orbit their star very quickly with a period of 2.25, 3.7 and 7.45 days. As Jonathan Brande, a co-author and astrophysicist at NASA Goddard and the University of Maryland, explained:

"If you have more than one planet orbiting in a system, they can gravitationally interact with each other. TESS will observe L 98-59 in sufficient sectors, so it may be able to detect planets with orbits about 100 days, but if we get really lucky, we can see the gravitational effects of undetected planets on those we know. "

Mens L 98-59b represents a new record for TESS, which is about 10% less than the previous record-holder it discovered, it's not the smallest exoplanet discovered to date. This record goes to Kepler-37b, a rocky exoplanet located about 210 light-years from Earth, which is only about a third of the Earth's size and 20% larger than the moon.

However, the discovery of L 98-59b is made more impressive when considering the fact that it orbits an M-type (red dwarf) star that is about one-third the size and mass of our Sun. This star is significantly less clear than Kepler-37, which is a G-type (yellow dwarf star) -like with our Sun – though L 98-59 is particularly bright as a red dwarf goes.

Combined with the fact that it is relatively close to our solar system, the discovery of a three-plane system around L 98-59 makes it an attractive candidate for follow-up observations. M-type stars are the most common type in the universe, which accounts for three-quarters of the stars in the winter street alone.

Recent studies have also shown that they may be the most likely place to find rocky planets that orbit within the star's habitable zone. Because of this, scientists are eager to learn more about the planetary systems that form around this type of star. These also include whether rocky planets orbiting red dwarfs would be able to maintain their atmospheres given the amount of radiation they would be exposed to.

Unfortunately, none of these planets circulate within the L 98-59's habitable zone. In fact, L 98-59b, at a distance from the mother star, receives as much as twenty-two times the amount of radiant energy that the earth comes from the sun. Meanwhile, L 98-59c and d receive approx. Eleven and four times as much radiation as earth.

But everyone occupies the "Venus Zone", the area distances, where a planet with an earth-like atmosphere could experience a continuous greenhouse effect, and transform it into a Venus-like atmosphere. Based on its size, L 98-59d can be either a Venus-like world or a mini-Neptune – like a rocky core surrounded by a dense gaseous envelope.

  An artist's illustration of Transiting Exoplanet Survey Satellite. Credits: NASA Goddard Space Flight Center
Artist's Illustration of Transiting Exoplanet Survey Satellite (TESS). Credits: NASA Goddard Space Flight Center

Whatever the case, there is still a chance that these planets may be potentially habitable, and ongoing research will answer vital questions about these and other rocky worlds that are near red dwarves – such as Proxima b and t h e seven-plane systems of TRAPPIST-1. As Joshua Schlieder, an astrophysicist at NASA Goddard and a co-author on the paper, stated:

"If we saw the sun from L 98-59, transits of Earth and Venus would lead us to believe that the planets are almost identical, but We know they are not, we still have many questions about why the Earth became habitable, and Venus did not. If we can find and study similar examples of other stars like L 98-59, we can potentially unlock Some of these secrets. "

Fortunately, TESS will have the opportunity to observe the system many times before the end of the month. Currently, TESS monitors 24 x 96 degree southern sky regions (aka Sectors) for 27 days at a time. When its first observation year ends in July, the L 98-59 system will have appeared in seven of the 13 sectors that make up the southern sky.

It hopes that this will allow astronomers time to refine what they know about these three confirmed planets, and perhaps to find more worlds in that system. Considering that all three circuits with the star's "Venus zone", something that bugs outside is likely to be in its habitable zone.

  Most exoplanets circle red dwarf stars because they are the most abundant stars. This is an artist's illustration of what the TRAPPIST-1 system can look like from a viewpoint near the plane TRAPPIST-1f (right). Credits: NASA / JPL-Caltech
The artist's illustration of what the TRAPPIST-1 system may look like from a vantage point near the planet TRAPPIST-1f (right). Credits: NASA / JPL-Caltech

These observations will also go a long way towards creating a catalog of rocky planets around nearby, bright stars. When the James Webb Space Telescope (JWST) takes place in 2021, it will use its advanced infrared imaging capabilities to gather information about the planet's atmosphere and characterize it.

Since four of the TRAPPIST-1 worlds orbits within their star's HZ, they are considered to be leading candidates. Kostov's team suggests that the L 98-59 planets are too. These combined efforts will effectively bring us a step closer to determining if there are any habitable planets in our cosmic neighborhood.

Additional reading: NASA

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