Astronomers discovered a surprising treasure around an orange dwarf star located 130 light-years away from Earth.
Three rocky super-Earth planets orbit the star, and two additional exoplanets exist in the system. This is almost unprecedented in our records.
These are super-Mercuries. This type of exoplanet is so hard to find that we have only eight (including the new ones).
The five exoplanets found are too close to the host star to sustain life as we know. However, this discovery provides the best laboratory to learn more about super-life. Mercury exoplanets – and Mercury itself, right here in the Solar System.
“For the first-time, we have discovered a super-Mercury system,” says astrophysicist Susana Barrosof the Institute of Astrophysics and Space Sciences, Portugal. This allows us to get clues about the formation of these planets, which may help us exclude certain possibilities.”
Finding exoplanets can be difficult, and it is even more difficult to find small ones. Astronomers currently rely on two methods: the transit method or the radial velocity.
For the transit method, astronomers will look for very faint, regular dips in the light of a star – the sign of an orbiting exoplanet passing between us and it.
Radial velocity looks for variations in wavelengths of light that reach us from the star, as it “wobbles”, tugged around by the gravitational force of an orbiting planet.
As you can imagine, both these signals – transit and radial velocity – are tiny. Larger exoplanets will produce more signals.
NASA’s exoplanet hunter telescope TESS (which uses the transit method) first detected two exoplanets orbiting star HD 23472. A few years backThey were confirmed by subsequent observations. Two additional exoplanet candidates were also found.
Barros and her colleagues wanted to look closer at HD 23472 in order to better understand it. Small planet radius gap: An enigmatic lack of planets with 1.5 to 2 Earth radii. Two of the confirmed exoplanets were at the upper end of the gap while the candidates were closer to the bottom.
Astronomers think that the atmosphere’s presence or absence could explain the differences. If you have both transit velocity and radial velocity data, you can calculate the density for an exoplanet.
The transit data can be used to determine the size of the star. This tells how much of a star’s light is blocked or blocked by an extraplanet. Radial velocity data can be used to determine the star’s mass. It shows how much gravitational pull an exoplanet exerts on it. These two measurements can be used to calculate density.
Between July 2019 and April 2020, the team attempted to obtain very precise radial velocity measurements using the ESPRESSO spectrograph at the European Southern Observatory’s Very Large telescope. They discovered evidence of a fifth exoplanet, with a mass lower than Earth, close to the star.
TESS received the transit signature of the fifth exoplanet, October 2021.
The team calculated all the numbers and characterised the system. From the nearest star to the furthest:
- HD 23472 D has an orbital time of 3.98 days. It also has a radius of 0.75 times Earth’s and a mass of 0.54 times Earth’s.
- HD 23472E e is the most recent discovery. It has a 7.9 day period and is 0.82 Earth Radii and 0.76 Earth Masses.
- HD 23472 has a 12.16-day duration and clocks in with 1.13 Earth radii, and 0.64 Earth masses.
- HD 23472b b has an orbital period of 17.67 days, is 2.01 Earth Radii and 8.42 Earth Masses.
- HD 23472 C has an orbital time of 29.8 Days, is 1.85 Earth mass and 3.37 Earth radiation.
These measurements yield densities that are comparable with Earth for the three outer exoplanets. They also indicate significant atmospheres.
These two exoplanets have high densities. These two exoplanets may have a similar composition to Mercury, with a large core but a smaller mantle than other planets.
Mercury’s behavior is not known. It could be that it collided early in the Solar System with material that literally knocked out a lot of material, or that the heat from the Sun evaporated some of it.
The fact that two of them are together indicates that it is possible for a singular event, such as a collision, to occur.
“It seems highly unlikely that a super-Mercury would be created by an impact as large as two huge impacts on the same system, even though it is very unlikely.” Barros explains.
We don’t yet know how these planets form, but we do know that it is connected to the composition the parent star. This new system could help us to find out.
It isn’t clear if the candidate super-Mercuries have atmospheres. To find out, we will need a larger telescope.
“Determining how these super-Mercuries formed will require additional characterization of the compositions of these planets,” says IA astronomer Olivier Demangeon.
“The radii of these planets are smaller than Earth’s, so current instrumentation doesn’t have the sensitivity necessary to probe their composition or detect the existence of an atmosphere.”
Consider the sheer number of Large telescopesCurrently under construction. We won’t have to wait too long, hopefully.
The results of the research by the team have been published in Astronomy & Astrophysics.
