Wow! An Actual Picture of Multiple Planets Orbiting a Sunlike Star

We’ve detected thousands of exoplanets, but for the most part, nobody’s ever seen them. They’re really just data, and graphs of light curves. The exoplanet images you see here at Universe Today and other space websites are the creations of very skilled illustrators, equal parts data and creative license. But that’s starting to change.

The European Southern Observatory’s Very Large Telescope (VLT) has captured images of two exoplanets orbiting a young, Sun-like star.

These images are part of a study titled “Two Directly Imaged, Wide-orbit Giant Planets around the Young, Solar Analog TYC 8998-760-1.” Lead author is Alexander Bohn, a PhD student at Leiden University in the Netherlands. The research is published in The Astrophysical Journal Letters.

The star is called TYC 8998-760-1. It’s about 300 light years away, and while it’s similar to our Sun, it’s younger; only 17 million years old. That means that in some ways, at least, it’s like looking at our Solar System in its younger days.

This chart shows the location of the TYC 8998-760-1 system. This map shows most of the stars visible to the unaided eye under good conditions and the system itself is marked with a red circle. Image Credit: ESO

“Our team has now been able to take the first image of two gas giant companions that are orbiting a young, solar analogue,” said co-author Maddalena Reggiani, in a press release. Lead author Bohn added “This discovery is a snapshot of an environment that is very similar to our Solar System, but at a much earlier stage of its evolution.”

Actual images of exoplanets are very rare, and this is only the third image of two exoplanets orbiting their star, and the first image of two orbiting a Sun-like star. Besides being a rarity, these images will have increasing scientific importance. “Even though astronomers have indirectly detected thousands of planets in our galaxy, only a tiny fraction of these exoplanets have been directly imaged,” said co-author Matthew Kenworthy, Associate Professor at Leiden University. He added that “direct observations are important in the search for environments that can support life.”

Could these two planets support life? Not likely.

Both of these planets are gias giants, and they orbit their star at distances of 160 and 320 AU. These planets are much further away from their star than Jupiter and Saturn are from our Sun. The two are also more massive than Jupiter and Saturn, with the closer one having 14 Jupiter masses and the further one six Jupiter masses. There’s probably a better chance of finding habitable conditions on any moons these two might have, much like some of Jupiter’s moons in our system.

In the images, the host star is in the upper left, while the two gas giants form a line down and to the left. White arrows mark the planets. By taking multiple images of the system at different times, they were able to rule out which dots were background stars, and which were planets.

This image, captured by the SPHERE instrument on ESO’s Very Large Telescope, shows the star TYC 8998-760-1 accompanied by two giant exoplanets, TYC 8998-760-1b and TYC 8998-760-1c. This is the first time astronomers have directly observed more than one planet orbiting a star similar to the Sun. Image Credit: ESO/Bohn et al, 2020.

The ESO’s VLT helped make this discovery with a special instrument called SPHERE, or Spectro-Polarimetric High-contrast Exoplanet REsearch instrument. Direct imaging of exoplanets is extremely difficult, but that’s what SPHERE was designed and built for. Normally, the bright light from a star makes it difficult to see the dim planets orbiting it, but SPHERE’s coronagraph makes it possible.

And future telescopes will be even better at imaging exoplanets. The ESO’s Extremely Large Telescope (ELT) should see first light in 2025, and will be even more powerful than the VLT.

The team learned a few things about these planets from these images. They think that the circular orbits are relatively stable, but there’s chaos on longer time-scales. That tells them something about how they formed, and if there might be other, as yet unseen, planets in the system. In their paper they write, “We show that circular orbits are stable, but that mildly eccentric orbits for either/both components (e > 0.1) are chaotic on gigayear timescales, implying in situ formation or a very specific ejection by an unseen third companion.”

Future observations with the ELT, or other facilities, should confirm of exclude the presence of other planets.

“The possibility that future instruments, such as those available on the ELT, will be able to detect even lower-mass planets around this star marks an important milestone in understanding multi-planet systems, with potential implications for the history of our own Solar System,” said lead author Bohn.

Emphasizing that point, the authors write in their paper that, “These multiplanet systems are intriguing laboratories to study dynamical interactions and scattering events between several planetary-mass companions, which is crucial for understanding the formation and dynamical evolution of planetary systems.”

This figure from the study shows the young, Sun-like star and its two exoplanet companions. Though not as compelling as some artist’s illustrations, which are designed to capture the imagination, images like these are data-rich. Each of the six panels are images of the star and its planets with different data reductions applied. In the lower left of each image, inside its own box, is the noncoronagraphic flux PSF (Point Spread Function), that tells astronomers about the filtering used. It’s kind of complicated for non-scientists, which is why professional illustrators are often used to help people understand discoveries like these. Image Credit: Bohn et al, 2020.

This system is ripe for further study. In their paper the authors write that this system is a “prime system to further study the dynamical and chemical properties of two coeval, gravitationally bound, gas giant planets.”

But to understand more about how they may have formed, and by extension learn something about how our own Solar System formed, researchers need to better constrain the orbits of the two planets. “Continuous astrometric monitoring will constrain the orbital solutions for both companions and thus enable testing of potential formation scenarios.”

The powerful SPHERE instrument made these images possible. But even SPHERE has its limitations. Its coronagraph is able to block out the bright light of the star and make the dim planets visible. Sadly, this only works in younger solar systems like this one. In ones like ours, the planets are too cool to be seen. The young planets in this system are hotter, and so they’re brighter in the infrared, making them visible.


Evan Gough

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