An inner solar system much like ours, 35 light-years away
A solar system much like ours
Astronomers have found more than 4,000 exoplanets, worlds orbiting distant stars in our Milky Way galaxy. Many reside in planetary systems vastly different from ours. But, on August 5, 2021, astronomers said they’ve found a distant planetary system that has intriguing similarities to our sun’s inner solar system. One of the planets is about half the mass of Venus, the planet next-door to Earth. Another could have oceans. And there might be yet another rocky world in this system’s habitable zone.
These astronomers used the European Southern Observatory’s Very Large Telescope to make their observations. The researchers published a new paper detailing their discoveries in the peer-reviewed journal Astronomy & Astrophysics on August 3.
It has 4 or 5 rocky planets
The host star, L 98-59, is only 35 light-years away. It has at least four confirmed rocky planets and possibly a fifth. That’s similar to our solar system’s rocky worlds (Mercury, Venus, Earth, Mars). But, in the L 98-59 system, the distance scales are different. And, by the way, all the known planets of L 98-59 are categorized as super-Earths. That means they’re rocky worlds larger in size than Earth, but smaller than Neptune.
One planet is half the mass of Venus
The innermost planet, L 98-59b, is only about half the mass of Venus. It’s the lightest exoplanet found so far using the radial velocity method. That technique measures the tiny “wobble” of a star caused by the gravitational tug of unseen orbiting planets. L 98-59b is probably quite dry. But it could have small amounts of water, according to the researchers. Its mass is only 1.01 times that of Earth, so very, very similar. It orbits its star in only 2.3 days, though!
The second planet is labeled L 98-59c. Its mass is 2.42 times that of Earth, and it orbits in 2.7 days.
An ocean world?
The third planet is where things get really interesting. It’s labeled L 98-59d. The researchers have calculated that up to 30% of this world’s mass is likely water. If so, it’s an ocean world. It’s not known yet how similar L 98-59d might be to Earth in terms of its oceans. But it does tickle the mind. Is this world’s water on the surface? Or is it mostly below ground? This planet has a mass 2.31 times Earth’s. It orbits its star in 7.5 days.
The newest-known planet in this system is the fourth planet, L 98-59e. It has a mass 3.06 times that of Earth and orbits its star in 12.796 days.
So you can see that all of these four worlds are really speeding around their star!
A rocky world in the habitable zone?
But there’s more. There’s new evidence for a fifth planet, labeled L 98-59f. Though still unconfirmed, this fifth planet is estimated to have 2.56 times Earth’s mass. It orbits in 23.15 days. What a slowpoke, right? The fact is, like all the other worlds in this star system, L 98-59f is still quite close to its star. But here’s something we haven’t told you yet. The star L 98-59 is a small and cool red dwarf star, one of the most common sorts of stars in our Milky Way galaxy. And that means its fifth planet orbits smack in the middle of the star’s habitable zone. The habitable zone – sometimes called the Goldilocks zone – isn’t too warm or too cool. It’s the region around a star where temperatures are just right for liquid water to exist on the surface of rocky planets.
We have hints of the presence of a terrestrial planet in the habitable zone of this system.
Co-author María Rosa Zapatero Osorio added:
The planet in the habitable zone may have an atmosphere that could protect and support life.
The role of ESPRESSO
How did the astronomers make these observations? They used the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) instrument on VLT to study L 98-59. ESPRESSO was essential, as Zapatero Osorio explained:
Without the precision and stability provided by ESPRESSO this measurement would have not been possible. This is a step forward in our ability to measure the masses of the smallest planets beyond the solar system.
NASA’s Transiting Exoplanet Survey Satellite (TESS) found the system’s first three planets in 2019. It found them using the tried-and-true transit method, where a planet is detected as it passes in front of its star as seen from Earth. But ESPRESSO was able to find the other one or two planets a bit farther out from the star. It also enabled the scientists to measure the masses and radii of the first three planets for the first time. Demangeon said:
If we want to know what a planet is made of, the minimum that we need is its mass and its radius.
So what’s next?
The HIRES instrument on the Extremely Large Telescope may have the power to study the atmospheres of some of the planets in the L 98-59 system, thus complementing the James Webb Space Telescope from the ground.
As Demangeon also noted:
This system announces what is to come. We, as a society, have been chasing terrestrial planets since the birth of astronomy and now we are finally getting closer and closer to the detection of a terrestrial planet in the habitable zone of its star … [when we find one,] we could study the atmosphere.
Bottom line: A team of astronomers using the Very Large Telescope has made new observations of a fascinating nearby planetary system. One planet is half the mass of Venus, another may be an ocean world and another possible planet resides in the habitable zone.