Since its launch in April 2018, TESS, the Transiting Exoplanet Survey Satellite, has located 5,969 candidate exoplanets within the immediate (cosmically speaking) neighbourhood of our solar system. Of these, 268 have been confirmed as actual planets – although 1,720 have been dismissed as false positives.
Three of the positives were located orbiting a red dwarf star called TOI 700, some 100 light-years away and within the constellation Dorado, one of which sits within the star’s habitable zone where liquid water might exist on the surface.
And now a fourth has been added to the tally, with the confirmed discovery of TOI 700-e, another planet within the star’s habitable zone. Like TOI 700-d, the other planet within the star’s habitable zone, it is roughly Earth-sized – around 95% the size of Earth, marking it as slightly smaller than TOI 700-d, which is 1.1 times the side of Earth.
This is one of only a few systems with multiple, small, habitable-zone planets that we know of. That makes the TOI 700 system an exciting prospect for additional follow-up. Planet e is about 10% smaller than planet d, so the system also shows how additional TESS observations help us find smaller and smaller worlds.
– Emily Gilbert, NASA’s Jet Propulsion Laboratory
TOI 700-d was actually the first Earth-sized planet TESS located within the habitable zone of s star, and wobbles in its orbit, and those of the other two planets TOI 700-b and TOI 700-c, led Gilbert and her team to task TESS with a re-visit to the system in the belief another planet might be hidden within it, hence the discovery of TOI 700-e.
All of the planets are likely tidally locked to their star – always keeping the same side facing it as they make their orbits. This makes the chances of them supporting life complicated, as one side is always exposed to the heat of the star, and the other to the freezing cold of space. Between them, along the terminator, they may have more temperate regions, but assuming the planets have an atmosphere, the temperate regions could be ravaged by storms where warm and cold fronts continuous meet. All four planets have short orbital periods – 10 days for the innermost planet 700-b to just over 37 days for the newly-discovered 700-e. Planets b, d, and e are likely rocky, while planet c is likely more similar to Neptune.
The term habitable zone also deserves some expansion, as it actually covers two overlapping zones around a star, the optimistic habitable zone (OHZ) and the conservative habitable zone (CHZ). The former is a region around a star where water may have existed at some point in the planet’s history; the CHZ is a more tightly-constrained region where scientists hypothesize liquid surface water might have existed for most of a planet’s history and it may have developed a more Earth-like atmosphere. TOI 700-e is in the optimistic habitable zone for its star.
That said, determining the habitability of solid rocky planets within the OHZ / CHZ of a star is impossible at our stage of exoplanet science. Simply put, they are fat too small to be seen well enough to make firm conclusions. All scientists can say is that a planet might be potentially habitable and then explain their detailed findings. In the case of TOI 700-e, the science team notes:
With a radius of 0.953 Earth radii, TOI-700-e is likely a rocky planet with a probability of 87%, [and a] timescale for tidal locking of to be on order a few million years. Given the age of the system, it is likely that the planet is in a locked-in synchronous or pseudo-synchronous rotation.
– Emily Gilbert, NASA’s Jet Propulsion Laboratory
One interesting aspect of the TOI 700 system is that while the star in an M-type red dwarf, a spectral type known for violent, powerful flares which could play havoc with the atmosphere and environment of the planets orbiting it. However, TOI 700 is older and more quiescent than its siblings and so perhaps less violent towards its children. Given this, and the fact it is a multi-planet system with two Earth-sized planets sitting within it OHZ, it forms a counterpoint to TRAPPIST-1, a younger, more aggressive M-class star with seven Earth-sized planets orbiting them, four of them within its own OHZ. Studies of both systems offers the potential for extended comparative study, potentially helping scientists better understanding of exoplanet systems form and M-type stars (the most numerous type of star in the galaxy), and how the planets within them retain (or lose) their atmospheres.
The discovery of TOI 700-e is a further demonstration on how the search for exoplanets is progressing. Prior to the launch of the long-running Kepler Space Telescope, only a handful of exoplanets had been discovered, and the number is now over 5,000, with discoveries in recent years revealing more and more Earth-sized worlds and multi-planet systems.
While the number of confirmed planets is small, TESS is adding to that total, and out ability to understand such worlds is gaining a boost thanks the James Webb Space Telescope (JWST). The instruments on the telescope are designed to study exoplanet atmospheres and use spectroscopy to determine their compositions. In fact, this work has already started with the planet Bocaprins (WASP 39b), a “hot Jupiter” planet 700 light years way, with JWST confirming its atmosphere contains sodium, potassium, carbon dioxide, carbon monoxide, water vapour and most significantly, sulphur dioxide.
The last is important both because it is the first time scientists have found this molecule anywhere outside of our Solar System, confirming photochemical reactions can take place in the atmospheres of exoplanets, and confirms JWST can detect such photochemical reactions within planetary atmospheres over vast distances – .something which could be an important factor in determining what interactions might be taking place in the atmospheres of many exoplanets.
As such, exoplanet science is maturing rapidly.
Soyuz MS-22 Update
Russia has confirmed it will launch Soyuz MS-23 to the International Space Station in an uncrewed mode to replace the Soyuz MS-22 vehicle which suffered a major coolant leak in December 2022, following what is theorised a piece of dust striking the external radiator at a speed of 7 km/s.
Following the accident, a number of western experts suggested the Soyuz vehicle would be incapable of maintaining a safe temperature in the crew cabin during a return to Earth. After a month-long review of the situation, including examining options for a space-based repair, the Russian space agency Roscosmos has reached the same conclusion.
Soyuz MS-23 will therefore launch on or around February 20th in an automated configuration to provide the means for cosmonauts Sergey Prokopyev and Dmitri Petelin and NASA astronaut Franco Rubio to return to Earth at a later date – exactly when that will be is unclear; as a result of needing to use MS-23 as a replacement vehicle, crew rotations on the Russian side of things will be disrupted, and so Roscomos expects the MS-22 crew to extend their stay on the station by “several months”.
However, the February launch for MS-23 still means that should an emergency evacuation of the station be required in the next month, the crew of MS-22 would be without a ride home. To cover this, it has been suggested at least one MS-22 crew member (likely Rubio) could return on Crew Dragon 5 with the four astronauts it flew to the ISS in October 2022, and remaining MS-22use that vehicle -the thinking at Roscosmos being that with a smaller crew, the damaged cooling system on the Soyuz wouldn’t be so strained and could maintain “safe” temperatures within the vehicle.
Once MS-23 has docked at the station, MS-22 will be prepared for an automated return to Earth, where the investigation into the coolant loss will continue.
Repairs to the damaged vehicle were ruled out due to the difficulties involved in any spacewalk to do so – not the least of which was the risk of ammonia contaminating the spacesuits used and then being brought back into the ISS in high enough concentrations that it might pose a serious health risk if inhaled by any of the crew.