Most of the exoplanets we’ve discovered have been identified by large surveys such as the Kepler mission or the mission Transiting a satellite to survey the outer planets (he-goat). While these projects are great at discovering stars that host planets, for the most part, they tell us that planets are out there. Understanding the outer solar system and its planets requires several follow-up observations – and the time of the telescope that accompanies them. over here , Huge success From the surveys it gave us a lot to note which we can easily access.
But follow-ups can provide important information, a study released this week shows. In it, the researchers describe observations of a three-planet system discovered by TESS. Using the additional observations, the researchers found that there are likely two other planets that TESS couldn’t see and that one it spotted is the least massive exoplanet described to date.
The system is called L 98-59, and it has two characteristics that make it a great candidate for follow-up observations. One advantage is that they are fairly close, at least from the perspective of galaxies, only 35 light-years from Earth. It’s also where it will spend a lot of time in the field of view of the James Webb Space Telescope, if this mission succeeds in reaching its operational orbit. This means that it will be relatively convenient to obtain sufficient images to study the atmospheres of the planets of the system.
TESS detects planets by observing the drop in light that occurs when planets pass between their host star and Earth. So others followed up this study with observations using radial velocity measurements, which monitor shifts in a star’s light that occur when the planet’s gravity pulls it in different directions. The radial velocity can give us the potential mass of the planet; Combined with the size of the planet provided by TESS, this can tell us about its density and thus provide hints about its composition.
Unfortunately, there was not enough time for the telescope to narrow the uncertainty much. The new paper presents several additional observations made with an instrument connected to the European Southern Observatory’s Very Large Telescope in Chile.
The standard means of analyzing this type of data is to identify the strongest periodic signal caused by a planet and remove it from the data, then continue to do so until the statistically significant signals are exhausted. Interestingly, when this analysis got to the point where the three planets identified by TESS were removed, there were still signals left. Signals indicated the apparent presence of a fourth planet – and the possibility of a fifth (models with four and five planets were equally consistent with the data).
What’s in L 98-59?
One of the obvious things to check is to see if other planets are visible, but whose signs have not been recognized. To verify this, the researchers relied on a program called (and I Don’t make this up) cAlculatioN or BATMAN. But in transit data, planets are not present.
This is not a big problem. Transits depend on a precise alignment of the outer system, with the planets rotating in a plane that intersects with the Earth. If not every planet orbits specifically within this plane, it may not travel from Earth’s perspective. However, it does mean that we either need additional data or careful analysis to look for gravitational interactions between planets, which can influence the timing of their transits.
If a fifth planet existed, its mass was two and a half times that of Earth, so it would likely be a rocky planet. It would also be in the middle of the habitable zone of L 98-59, where liquid water could exist on the planet’s surface. Because L 98-59 is a faint young star, the habitable zone is so close that the planet takes only 23 days to complete its orbit.
Since detecting the radial velocity tells us the mass of the planet and watching the transit of the planet gives us its size, we now know the density of the three planets detected in both ways. Two are somewhat less dense than Earth, indicating that they are similar in structure, except for the presence of a smaller iron core. By contrast, one-third is only about half the density of Earth, suggesting that it could be as much as 30 percent water – an ocean world.
Another startling discovery is the mass of an Earth-like planet. It’s less than half the mass of Earth, making the planet much larger than Mercury and Mars but less than half the mass of Venus. It is thus the smallest exoplanet discovered so far. Based on the solar system, we expect there to be a large number of planets this size or smaller, so it’s encouraging that we are finally discovering them.
At this point, there are thousands of candidate planets that we haven’t examined. Many similar surprises can await us. In the meantime, surveys like TESS will continue to add to the list of items we need to check more carefully.
Astronomy and astrophysics, 2021. DOI: Not yet available.