Direct imaging of a gas giant is not totally new. What is new is the combination of direct imaging with an indirect method that allows better understanding of the mass of gas giants in other solar systems. Knowing the mass of a planet is crucial to understanding what kind of world it is. For example, if we were talking about Earth-like planets, a more massive Earth would have gravity so strong that land could not build up as high as it does. The result would be a water world. A more massive Jupiter would not necessarily be bigger but merely denser. A denser Jupiter would have completely different internal dynamics. While gas giants may seem boring, they are bigger than Earth-like planets hence easier to study. Techniques that allow better understanding and which prove their worth studying gas giants will someday be applied to understanding a pale blueish dot around a Sun-like star sometime soon.

The fundamental difficulty of imaging planets is that they are not sources of light themselves but reflect the light of their star which is a bright glaring light source. It is not so much like seeing a firefly next to a spot light but like seeing the light reflected off an ordinary fly next to a spot light. Imaging a Jupiter mass and Jupiter diameter planet is like imaging a large dragonfly next to a spot light. An Earth mass and diameter planet would be more like a small fruit fly next to that same spot light.There are three basic methods for detecting a planet. One is to look for the gravitational influence of the planet on the star. Stars are far more massive than planets but the gravitational pull of the planet on the star as it orbits the star can be detected in the spectrum of light from the star. As the planet orbits, it will apply a Doppler shift to the spectrum of the star. For more massive planets, this is a much more noticeable effect. Another method is to observe the planet transiting the star. This happens when the planet’s orbit is aligned with our line of sight to the star. In this case, we observe a drop in the light from the star of less than 1%. These first two methods are examples of what is called astrometry. They involve observing the star to infer the existence of a planet by how the planet’s presence would affect the star. The third basic method is direct imaging which involves using methods that block or cancel out the light from the star leaving only the light from orbiting planets.As the paper says “These detections were made by blind (unbiased) surveys, in which targets were selected based on proper-ties of the stellar system, including age and distance. However, the low yields of these blind surveys have shown that exoplanets detectable with direct imaging are rare ”   So as part of an astrometry and imaging search for young exoplanets they looked at HIP 99770 and identified it has having astrometric acceleration due to the presence of a planet.  Direct imaging was done using the Subaru telescope which sits near the top of Mauna Kea in Hawaii.  They used a Coronagraphic high resolution imager to take a series of images of HIP 99770b  A planet that their data indicates orbits its star 14 times farther out than Earth orbits.

The first author also tweets this comparison to our solar system.

This is a great discovery of a new Jupiter like planet. This is also a great step to validate methods that will someday be applied to the study of more Earth like planets.  Planets which may be home to Earth like life, at some point in the future.

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Thayne Currie et al. ,Direct imaging and astrometric detection of a gas giant planet orbiting an accelerating star.Science380, 198-203(2023).DOI:10.1126/science.abo6192