2 Incredibly Rare Exoplanets Could Give Us Insights About a Planet Close to Home

Astronomers have found a treasure around an orange dwarf star.

Two more exoplanets in the system are almost impossible to find in our records.

These two are so difficult to find that we've only found eight of them.

All five exoplanets are too close to their host star for life as we know it to be possible, but the discovery represents the best laboratory yet for learning more about super-Mercury exoplanets.

Susana Barros is an astronomer at the Institute of Astrophysics and Space Sciences in Portugal. We can get clues about how these planets were formed.

It is difficult to find small exoplanets. Astronomers use the transit method and the radial velocity method.

Astronomers will look for faint dips in the light of a star that are signs of an exoplanet passing between us and it.

The radial velocity method looks for changes in the wavelength of light that reaches us from the star as it "wobbles" on the spot.

Both of these signals are very small. Bigger signals are more likely to be detected by us.

Two exoplanets were found a few years ago by NASA's exoplanet-hunting telescope TESS, and follow-up observations confirmed their existence. The two other exoplanet candidates were also found.

The HD 23472 system was being looked at by Barros and her team to understand the small planet gap. The two confirmed exoplanets were on the high side, while the two candidates were on the small side.

Astronomers think the difference may be in the atmosphere. If you have both transit and radial velocity data, it's possible to calculate the density of an exoplanet.

The transit data can give you the size of a star. The mass can be given by the radial velocity data. They can be used to calculate density.

The team decided to use the European Southern Observatory's Very Large Telescope to obtain very precise radial velocities of the star. There is evidence of a fifth planet in close proximity to the star.

The transit signature of this fifth exoplanet was picked up by TESS.

All the numbers were crunched by the team. The distance from closest to farthest.

• HD 23472 d has an orbital period of 3.98 days, a radius 0.75 times that of Earth, and a mass 0.54 times that of Earth.
• HD 23472 e, the most recent discovery, has a 7.9-day period, and is 0.82 Earth radii and 0.76 Earth masses.
• HD 23472 f has a 12.16-day period, and clocks in at 1.13 Earth radii and 0.64 Earth masses.
• HD 23472 b has a 17.67-day orbital period, and is 2.01 Earth radii and 8.42 Earth masses.
• HD 23472 c has an orbital period of 29.8 days, and is 1.85 Earth masses and 3.37 Earth radii.

The densities are similar to Earth for the three outer exoplanets.

Two inner exoplanets have high densities. It is possible that they are similar to Mercury in composition, with a large core and a small mantle.

We don't know why Mercury is this way, it could be that it hit something early in the Solar System that knocked a lot of material away, or that the heat of the Sun evaporated a lot of it.

It's possible that a one-off event like a collision isn't going to happen.

Two giant impacts in the same system seems very unlikely if an impact large enough to create a super Mercury is already very unlikely.

We don't know how these planets are formed, but we do know that they are related to the parent star. We can use this new system to find out.

We will need a bigger telescope to find out if the two candidates have atmospheres.

"Understanding how these two planets formed will require further characterization of the composition of these planets," says IA astronomer.

Current instruments do not have the sensitivity to probe the composition of their surface, or the existence and composition of a potential atmosphere.

Hopefully, we won't have to wait a long time.

The research was published in astronomy and astrophysics.