An article accepted for publication in “The Astrophysical Journal Letters” reports the discovery of the exoplanet TOI 700 e. A team of researchers used observations conducted with NASA’s TESS space telescope and confirmed with other instruments to find it. It’s the fourth planet discovered in the TOI 700 red dwarf system and is interesting because it’s a rocky planet a bit smaller than Earth. Its habitability potential is yet to be assessed because it’s within the so-called optimistic habitable zone, where a planet can only have liquid water on its surface for part of its history.
The star TOI 700 was observed by the TESS space telescope in the first year of its scientific mission as a planet hunter. The discovery of three exoplanets around it was announced in early 2020. It was particularly interesting because the one cataloged as TOI 700 d was at the limit of its habitable zone and it was the first of this type discovered thanks to TESS.
New observations of that system were conducted by the TESS space telescope in 2020 offering new information. More precise estimates of the size of the planets already identified showed that they’re smaller than initial calculations. This means that the exoplanet TOI 700 d is almost exactly as large as Earth. However, the most interesting result is the discovery of the trace of the possible transit of another exoplanet.
The new trace found was weaker than the traces of the already confirmed exoplanets but it was verified as well by conducting follow-up observations. Finally, new confirmations of another exoplanet arrived, cataloged as TOI 700 e. Data on it is still limited and includes an estimate of its size at about 95% that of Earth and the year at just under 28 Earth days.
The exoplanet TOI 700 e is too close to its star to be in the conservative habitable zone, where water on a planet’s surface can be liquid for most of its history. However, the optimistic habitable zone, where water may be liquid on its surface for part of its history, is wider and TOI 700 e falls within it as shown in the schematic in the top image schematic (NASA/Goddard Space Flight Center).
To estimate the habitability potential of the exoplanet TOI 700 e, other follow-up observations are needed with instruments that can offer information on its atmosphere. For the moment, we’re not even sure that it has an atmosphere and it will be necessary to study this planet and its star in-depth to understand if there may be liquid water on its surface right now.
Emily Gilbert of NASA’s Jet Propulsion Laboratory, the first author of the article and part of a team that participated in the discovery of the first exoplanets in the TOI 700 system, explained that new follow-up observations are ongoing. This system is relatively close, so the star is bright enough to allow in-depth studies of its planets and their possible atmospheres. Being able to evaluate the habitability potential of two rocky planets in the same system makes it one of the most interesting for astronomers.