Key Takeaways:

  1. Finding planets outside our solar system is difficult because stars are bright and planets are dim.
  2. Direct imaging is a technique astronomers use to look for exoplanets, but it’s difficult because planets are much fainter than stars.
  3. A new giant planet called HIP99770b has been discovered using a combination of direct imaging and astrometry.
  4. HIP99770b is a hot, giant planet that orbits its star at a distance similar to Saturn’s orbit around our Sun.
  5. The discovery of HIP99770b shows that combining astrometry and direct imaging is a more effective way to find exoplanets.

Discovering extraterrestrial life may be astronomy’s ultimate goal, but finding viable host planets where life can exist requires a lot of resources.

The largest telescopes on Earth are used to compete for time in the search for exoplanets, or planets outside of our solar system, but the success rate of this effort can be surprisingly low.

I have found a new giant planet with my international team of colleagues by combining various search methods in a study that was published in Science. It might alter our future attempts to visualize planets.

Planet imaging is a difficult task.

Astronomers have created numerous methods to look for planets orbiting other stars in order to satiate our curiosity about our place in the cosmos. Among them, direct imaging is undoubtedly the most basic. However, it’s not easy.

By mounting an effective camera on a sizable telescope, direct imaging involves attempting to identify light that is reflected or emitted from a planet. It’s like trying to find fireflies circling a spotlight because stars are bright and planets are dim.

It’s no surprise only about 20 planets have been found with this technique to date.

But in a way that other detection methods cannot, direct imaging provides valuable information about a planet’s atmospheric characteristics, including temperature and composition.

HIP99770b: a new gas giant

Based on our direct imaging of HIP99770b, we have discovered a hot, giant, and somewhat cloudy planet that orbits its star at a distance that is halfway between that of Saturn and Uranus around our Sun.

The HIP 99770 star is almost 14 times brighter than the Sun. But since its planet has an orbit larger than Saturn’s, the planet receives a similar amount of energy as Jupiter does from the Sun. Author provided

HIP99770b is a true giant with a mass of roughly 15 times that of Jupiter. However, it’s also more than 1,000°C, so it’s not a good prospect for a habitable world.

The HIP99770 system does, however, provide a solar system analogy. Far from the star, it has a chilly “debris disk” of rock and ice that resembles our solar system’s Kuiper Belt on a larger scale.

The primary distinction lies in the fact that the HIP99770 system is governed by a single massive planet, as opposed to multiple smaller ones.

Astronomers have directly detected a massive exoplanet. The method could  transform the search for life beyond Earth
Images of the HIP 99770 system, taken with exoplanet imager SCExAO (Subaru Coronagraphic Extreme Adaptive Optics Project) coupled with data from the CHARIS instrument (Coronagraphic High-Resolution Imager and Spectrograph). Author provided

Looking with the light on

We arrived at our conclusions by first using indirect detection techniques to find signs of a planet. We saw that the star moved in space, suggesting that a planet with a strong gravitational pull was nearby.

Our direct imaging efforts were now motivated by this; we were no longer stumbling around in the dark.

The additional information originated from the Gaia spacecraft of the European Space Agency, which has been tracking the locations of almost one billion stars since 2014. Gaia has the sensitivity to pick up on minute changes in a star’s motion through space, including those brought on by planets.

We also added measurements from Hipparcos, Gaia’s predecessor, to these data. We worked with “astrometric” (positional) data spanning a total of 25 years.

In the past, scientists have guided imaging by indirect means, which has found companion stars but not planets.

It’s not their fault; stars with massive masses, like HIP99770, nearly twice as large as the Sun, are reluctant to reveal their secrets. Otherwise-successful search techniques can rarely reach the levels of precision required to detect planets around such massive stars.

Our detection, which combined astrometry and direct imaging, shows a more effective method of planet hunting. For the first time, initial indirect detection techniques have guided the direct discovery of an exoplanet.

It is anticipated that Gaia will keep up its observations until at least 2025, and its archive will be valuable for many years to come.

There are still mysteries.

HIP99770’s astrometry indicates that it is a member of the Argus association, a star group that travels through space together. This would imply that the system is only 40 million years old, which is relatively young. Accordingly, it would be about a hundredth of our solar system’s age.

Nonetheless, models of the planet’s brightness and our examination of the star’s pulsations point to an older age of between 120 million and 200 million years. In such a scenario, HIP99770 may simply be an outsider in the Argus group.

Astronomers will work to further solve the mysteries surrounding HIP99770 and its immediate surroundings now that it is known to host a planet.

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