TOI 700 e is one of four known planets that orbit a cold star roughly 100 light-years distant. The planet was found by NASA’s Transiting Exoplanet Survey Satellite, a planet-hunting telescope.
Image: NASA/JPL-Caltech/Robert Hurt
The Transiting Exoplanet Survey Satellite (TESS), a NASA planet-hunting telescope, has identified a second Earth-size planet inside the habitable zone of a neighboring star.
The planet, TOI 700 e, is one of four known planets circling a cold star around 100 light-years distant. The system was previously known to have one planet in the habitable zone, dubbed TOI 700 d, but a new study published in the Astrophysical Journal Letters revealed it is joined by another planet within its orbit. TOI 700 b and TOI 700 c, the other two planets in the system, orbiting closer to the star and, as a result, are anticipated to have greater temperatures, pushing them outside of the habitable zone.
The new planet “is tucked in there between planets c and d, so I’m really sorry they’re not in alphabetical order,” one of the researchers, Emily Gilbert of NASA’s Jet Propulsion Laboratory, remarked at a briefing on Tuesday, January 10th at the American Astronomical Society conference.
Because planets are assigned letters based on their discovery date rather than their location within a system, there may be instances when closer-orbiting planets are found later than distance-orbiting planets.
The newly found planet TOI 700 e is located in the optimistic habitable zone, while the previously identified planet TOI 700 d is located in the conservative habitable zone. The classic notion of the habitable zone is a region around a host star where temperatures are high enough for liquid water to exist on a planet’s surface. This concept, however, is more difficult to implement in reality than it seems, which is why these researchers use the labels “optimistic” and “conservative.”
The optimistic habitable zone is a region where liquid water might have existed at some time in a planet’s history, while the conservative habitable zone is a narrower area within which planets would stay livable. These two differ due to a planet’s surface temperature — and hence whether water can exist in liquid form — and may fluctuate greatly over time depending on variables such as the thickness and makeup of a planet’s atmosphere.
This enlargement of the conventional habitable zone is “to account for the fact that we think Mars and Venus formerly had liquid water on their surfaces,” Gilbert stated,
alluding to evidence that both planets once had water. The study of planets in this hopeful zone increases the amount of possibly habitable worlds that astronomers may utilize to learn about the history of our own solar system.
Astronomers can also contrast the four planets in the TOI 700 system.
“We know that these planets originated under the same starting circumstances — they formed around the same star, from the same disk,” says Dr. Smolin.
“This allows us to explore how various planet features, such as planet size or the borders of the habitable zone, may impact planet habitability,” Gilbert said.
This system, like the TRAPPIST system, is one of the few known to hold several Earth-size planets inside its habitable zone. The finding was also announced the same day as LHS 475 b, another Earth-size rocky planet and the first exoplanet identified by the James Webb Space Telescope, or JWST. That planet, however, is significantly closer to its star and hence outside of the habitable zone. The TESS and JWST spacecraft collaborated to discover this new exoplanet, with TESS detecting a candidate exoplanet before JWST verified it.
We may anticipate further exoplanet discoveries from both telescopes in the future, and the TESS discovery team said they will continue to study the TOI 700 system to learn more about the habitable planets.
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