At about 1,410 light years away from us lies WASP-12b- one of the blackest planet in our galaxy. It orbits star WASP-12, a yellow dwarf star which is a little bigger than our Sun.
The exoplanet was discovered on 1 April 2008.
Belonging to “hot Jupiter” category, this ultra black exoplanet is a gas giant with similar size and mass of Jupiter. WASP-12b’s orbital period is just over an Earth day, meaning it is so close to its parent star that material from its atmosphere is constantly stripping off.
The gas giant exoplanet is also on a significantly decaying orbit. A recent study/research has revealed that the orbit is decaying a bit faster than what was thought previously.
Initially it was calculated that WASP-12b will meet its end in around 3.25 million years but the new research has estimated it to be just 2.9 million years.
As per our current scientific models of planet formation hot Jupiters shouldn’t exist. A gas giant planet can not form that close to its parent star as the radiation, gravity and strong stellar winds from star won’t let the gases to stick together.
But contrary to planet formation models, hot Jupiters do exist, in fact several hundred of them have been spotted in the exoplanet data.
WASP-12b is among the nearest hot Jupiters to its parent star. Hot Jupiters particularly that close are best to study the tidal interactions between a planet and its star.
Due to exoplanet’s short orbital period a lot of transits (when exoplanet passes between us and star, slightly dimming the star light) can be observed, meaning more data to study the planet.
In 2017 scientists noticed that WASP-12b’s transits were occurring just a fraction of a second off as compared to previous measurements of the orbital period.
This small time variation could have been because of the gas giant’s orbit changing direction. This prompted a team of scientists led by Samuel Yee of Princeton University to study the planet in more extensive details.
The team closely monitored the transits and occultations (when exoplanet passes behind the star). If exoplanet was indeed changing direction then the occultations should be slightly delayed.
A transit causes a slight dim in star light, whereas an occultation causes an even more fainter dim. That’s because when exoplanet is not behind the star, it adds to system’s overall brightness while reflecting the star’s light and heat.
WASP-12b optically absorbs ninety four percent of the light that it receives from its parent star. That makes it very dark, even blacker than asphalt.
According to scientists this is because at temperature of about 2,600 degrees Celsius on the day side, hydrogen molecules are torn apart into atomic hydrogen, causing the planet’s atmosphere to behave like a low mass star. And since it is so hot, it glows in infrared.
Study team used the Spitzer Space Telescope to observe the occultations. Team observed the exoplanet and star for sixteen orbital periods but could only managed to obtain four faint occultations in the data, and as per team that was enough.
Team found out that the occultations were occurring more rapidly. This was consistent with an orbital decay of twenty nine milliseconds per year. At this rate exoplanet’s lifespan was calculated to be around 3.25 million years.
And now, a team of scientists led by Jake Turner from Cornell University searched for signs of orbital decay in the observation data from NASA’s Transiting Exoplanet Survey Satellite (TESS).
TESS has observed the portion of the sky that included WASP-12 from December 24, 2019 to January 20, 2020. Going through this data, team found twenty one transits while occultations were too shallow to identified individually. But the team managed to model these occultations to find a best fit for TESS data.
For timing analysis, team combined these transit/occultation times with the previous data. Results confirmed that WASP-12b’s orbit is definitely decaying but a little faster than previously thought.
Newly calculated orbital decay rate is 32.53 milliseconds per years, meaning the exoplanet has a total lifespan of 2.9 million years.