Discovery of two potentially habitable super-Earths located just 100 light years away

Discovery of two potentially habitable super-Earths located just 100 light years away

Discovery of two potentially habitable super-Earths located just 100 light years away

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Hundreds of exoplanets have been detected since 1995, revealing that most of the stars in our galaxy are home to their own planetary system. Some of them host planets located in the habitable zone of their star, which motivates the space search for other life forms. Recently, an international team discovered two super-Earths in the habitable zone of the red dwarf LP 890-9. One of these could be the second most habitable exoplanet discovered so far.

In the era of the James Webb Space Telescope, temperate terrestrial exoplanets transiting in ultra-cold red dwarfs offer unique opportunities to characterize their atmospheres, as well as to search for gas biosignatures. The goal is to understand how often and under what conditions life can appear.

It is for this purpose that the SPECULOOS project (“Search for habitable Planets EClipsing ULtra-cOOl Stars”) was created. Although SPECULOOS officially began its scientific operations in 2019, it was launched in 2011 as a prototype survey targeting fifty of the brightest red dwarfs on the south side with the TRAPPIST South telescope. This investigation prototype led to the discovery of the TRAPPIST-11 system, consisting of seven terrestrial planets passing through a nearby ultracool dwarf M8V.

The discovery of this reference system sparked a wave of theoretical and observational follow-up studies, so much so that the TRAPPIST-1 planets are today the best studied terrestrial planets outside our solar system. In fact, the authors of this discovery stated in a 2017 statement: ” The Trappist-1 system is the largest treasure trove of Earth-sized planets ever detected around a single star “.

Recently, an international team of scientists, led by Laetitia Delrez, astrophysicist at the University of Liege, just announced the discovery of two “super-Earth” type planets orbiting a dark red dwarf star, TOI-4306. It is the second coldest star around which planets are detected, after TRAPPIST-1, located about one hundred light years from our Earth. These rocky planets are slightly larger than Earth and appear habitable. Indeed, one of these may be the second most habitable exoplanet discovered to date. This work is published in the journal Astronomy and astrophysics.

Discovery in synergy

This detection of two temperate super-Earths passing through the nearby dwarf star LP 890-9 was fortuitous. In fact, the innermost planet (TOI-4306.01) was first detected by TESS. This announcement triggered intensive photometric monitoring by the Southern SPECULOOS Observatory, which led to the discovery of a second long-term transiting planet, previously not detected by TESS.

In concrete terms, the first planet is about 30% larger than Earth and completes a full orbit around the star in just 2.7 days, too fast to sustain life there. ULiège researchers used their ground-based SPECULOOS telescopes to confirm and characterize this planet, and also probe the system deeply for other planets.

Laetitia Delrez, FNRS researcher in the research units Astrobiology and STAR (Faculty of Sciences) of the ULiège, and principal author of the study, explains in a statement: ” TESS searches for exoplanets using the transit method, monitoring the brightness of thousands of stars at once, looking for small dips in light output that could be caused by planets passing in front of their stars “.

However, the use of ground-based telescopes is essential to confirm the telluric nature of the findings and to allow for precise measurements of orbital size and properties. This tracking is particularly important in the case of very cold stars, such as LP 890-9, which emit their light mainly in the near infrared and for which TESS has only limited sensitivity.

For this reason, the SPECULOOS telescopes, directed by ULiège and installed within the European Southern Observatory (ESO) of Paranal in Chile (SPECULOOS south) and the Teide Observatory of Tenerife (SPECULOOS north), aim to detect terrestrial planets that eclipse some of the smallest and most beautiful stars in the solar quarter. They are equipped with very sensitive near infrared cameras.

Michaël Gillon, senior FNRS researcher, co-director of the astrobiology research unit at ULiège, states: ” The purpose of SPECULOOS is to search for potentially habitable terrestrial planets that pass around the smallest and coolest stars in the solar neighborhood, such as the TRAPPIST-1 planetary system, which we discovered in 2016 through a pilot project with our TRAPPIST telescope. “.

A planet close to the characteristics of the Earth

Therefore, observations via SPECULOOS allowed to confirm the first planet, but also to detect a second one as mentioned above. This second planet, LP 890-9c (renamed SPECULOOS-2c by ULiège researchers), is similar in size to the first – about 40% larger than Earth – but has a longer orbital period of about 8.5 days. This orbital period, later confirmed with the MuSCAT3 instrument in Hawaii, places the planet in the so-called “habitable” zone around its star.

Comparison between the LP 890-9 system and the inner solar system. The LP 890-9 system is much more compact: its two planets could easily fit into the orbit of Mercury, the innermost planet in our solar system. © Adeline Deward (RISE-Illustration)

Francisco J. Pozuelos, researcher at the Astrophysics Institute of Andalusia, points out: ” Although this planet is very close to its star, at a distance about 10 times shorter than Mercury’s around our Sun, the amount of stellar radiation it receives remains low, and could allow liquid water to be present on the planet’s surface, as long as has a sufficient atmosphere “.

This potential presence of liquid water would be mainly due to the fact that the star LP 890-9 is about 6.5 times smaller than the Sun and that it has a surface temperature of half the size. In facteven if the planet is closer, it still has “conditions suitable for life”.

Next, the researchers want to study this system, in particular SPECULOOS-2c, using the James Webb space telescope to characterize its atmosphere, as has recently been the case for the exoplanet WASP-39b. As Laetitia Delrez points out, unlike the planets of the TRAPPIST-1 system, we must take into account that ” LP 890-9c is located near the inner limit of the habitable zone and could therefore have an atmosphere particularly rich in water vapor, which would increase its atmospheric signals. “.

The authors conclude: The discovery of LP 890-9c offers a unique opportunity to better understand and constrain the habitability conditions around the smallest and coldest stars in our solar neighborhood “.

Source: astronomy and astrophysics

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