When it comes to finding life outside of our solar system, planets very similar to Earth seem like a good place to start. We can now welcome the celestial object TOI 700 e to this group of promising clues.
TOI 700 e has been confirmed in orbit habitable zone its star TOI 700. This is the region of space where significant amounts of water on its surface would be at a temperature suitable for liquid form. Too warm for an ice sheet but still cool enough to condense vapor, these planets are considered “just right” for life as we know it.
We can thank NASA’s Transiting Exoplanet Survey Satellite (TESS) for finding and naming TOI 700 e (TOI means TESS Object of Interest). It is the second planet in the habitable zone in this system, joining TOI 700 d, which was then 2020 spotted.
“This is one of only a few systems with multiple small planets in habitable zones that we know of,” says planetary scientist Emily Gilbertfrom NASA Jet Propulsion Laboratory (JPL) in California.
“This makes the TOI 700 system an exciting prospect for further follow-ups. Planet e is about 10 percent smaller than planet d, so the system also shows how additional TESS observations are helping us find smaller and smaller worlds.”
TOI 700 is a small, cool star (known as the M dwarf star) located about 100 light-years from us in the constellation Dorado. These stars aren’t nearly as big or as hot as our own sun, so the planets need to be closer to them for conditions to be warm enough for the water not to freeze.
As for TOI 700 e, it is thought to be 95 percent the size of Earth and is mostly rocky. It is in the “optimistic” habitable zone – a zone that may have had water at some point in time. TOI 700 d is in the narrower “conservative” habitable zone, where astronomers believe liquid water could exist for most of a planet’s existence.
Telescopes see these exoplanets (planets outside of our solar system) as regular blips in the light of their parent stars as they pass, in what is called a transit. With more surface area blocking the star’s light, larger planets offer easier opportunities to be seen than small, rocky worlds, making Earth-like discoveries like this a rare treat.
TOI 700 e needs 28 days for an orbit, TOI 700 d – slightly further away than its neighbor – 37 days. Because TOI 700 e is smaller than TOI 700 d, more data was needed to confirm that the silhouette truly represents a new planet.
“If the star had been a little closer or the planet a little bigger, we might have detected TOI 700 e in the first year of TESS data,” says astrophysicist Ben Hord from the University of Maryland. “But the signal was so weak that it took us the extra year of transit observations to identify it.”
TESS monitors about 100 million stars, so any way we can find to narrow down the search for life will be useful. Finding exoplanets in their respective habitable zones is one of the best ways we have for that.
Both TOI 700 e and TOI 700 d are believed to be tidally dependent: in other words, one side of the planet always faces its star (as does the same side of the moon is always visible from Earth). Admittedly, when one side of a planet is constantly burning in sunlight, complex life is less likely to get off to a smooth start.
While these “just right” planets aren’t exactly perfect for life, they tell us a thing or two about finding solar systems that might be better suited. By studying star systems like the one we are in, astronomers can also better understand the evolution of our homeland and how neighboring planets got into their current orbits.
“Even with more than 5,000 exoplanets discovered to date, TOI 700 e is a key example that we still have much more to learn.” says astronomer Joey Rodriguez from Michigan State University.
The research paper was accepted for publication in the Astrophysical Journal Lettersand is currently available for viewing arXiv.
