Nearly 100 light-years away, a world 95% of Earth’s size orbits its star in the endless void. The distant exoplanet, which lies in a habitable zone that allows liquid water to form on its surface, existed in relative obscurity to NASA and its team of scientists, until now.
The discovery of exoplanet TOI 700 e, one of four planets found orbiting dwarf star TOI 700 in the southern constellation of Dorado, was made by NASA’s Transiting Exoplanet Survey Satellite (TESS).
“One of the primary goals of TESS is to be what people have been calling a finder scope for JWST (James Webb Space Telescope), so it’s effectively a scout to find planets that we think would be good targets to characterize their atmospheres,” said Emily Gilbert, a postdoctoral fellow at JPL who led the work to find TOI 700 e. “TESS is looking at the nearest brightest stars, looking for targets that we think are most amenable for follow up.”
TESS finds exoplanets by monitoring large expanses of the sky for around 27 days at a time, allowing the satellite to track changes in stellar brightness that are caused by a planet’s transit, when it moves in front of its star.
“(TOI 700 e’s) signal was originally picked up by the TESS planet search pipeline,” Gilbert explained. “Those signals can include lots of false positives and other non-planet things, so once you have this proposed signal you have to go in and make sure that it’s real and confirm it and model the data. Once you do that, you can determine a fair number of planet properties. Then you can use that to learn more about the planet, figure out how big it is, learn about the orbit and place it in the context of the system and in the context of all of the exoplanets that we know.”
The mission had previously discovered the three other planets in the TOI 700 system. TOI 700 b is roughly 90% of Earth’s size and orbits the star every 10 days. TOI 700 c is over 2.5 times bigger than Earth and orbits every 16 days, while TOI 700 d is Earth-size and joins TOI 700 e in the habitable zone.
“Having multiple planets in the habitable zone lets us compare some of those properties (like temperature and size) and see what we think might end up really mattering for planet habitability,” Gilbert said. “There’re only a few other systems like this and it’s really hard to follow up a lot of these systems. And so that’s really exciting to me.”
Gilbert expressed hope that her team can expand their current data on the TOI 700 system to include radial velocity measurements of the star, which could be used to calculate the planets’ masses. Knowing the mass and the radius, Gilbert’s team could find the composition for each planet.
“There are a ton of people who put work into projects like this; it’s really a big collaborative effort,” Gilbert said. “We have some of the people who spend a lot of time on the data reduction and the modeling and all of the pipelines from TESS … even just building the TESS spacecraft and all of the infrastructure required for that. Then on top of that, we have people who are ground-based observers who are contributing follow up that we use as a part of the TESS Follow-Up Observing Program called TFOP.
“You’ll see on any of these big TESS discovery papers, the author lists are dozens of authors long because it really takes a whole community in order to confirm these planets.”
Gilbert insisted that this discovery will become one of many more significant findings as TESS slowly fills patches of sky that have never previously been observed. She described the onrush of new internal discoveries and external attention as “overwhelming.”
“I love seeing all of the news coming out about this,” Gilbert said. “It’s not very often that your research is something that excites the general public. Seeing people who are not astronomers get really excited about this discovery too, it’s really amazing.”