A doomed egg-shaped exoplanet spirals toward its star

Astronomers have discovered that a distant, scorching-hot planet twice the size of Jupiter is in a death spiral that will send it spiraling toward its parent star. Cosmically, a crash is expected to occur relatively soon.

Researchers have been predicting for some time that this planet, called WASP-12b, will eventually plunge into its star located about 1,400 light-years from Earth. However, these new findings have shortened the remaining time of WASP-12b.

Previous estimates put WASP-12b about 10 million years before its inevitable demise, but these researchers say it’s more likely the planet collided with its star much earlier.

‘According to our calculations the planet will collide with the star [WASP-12] in just 3 million years, an incredibly short time considering the star appears to be only 3 billion years old,” Pietro Leonardi, lead author of the study and scientist from the University of Padua, told Space.com.

In other words, this may seem incredibly long, but the fact that stars like the Sun live for about 10 billion years means that on a cosmic scale this is a very (very) short period.

Related: Small 14-inch satellite studies ‘hot Jupiter’ exoplanets evaporating into space

WASP-12b is getting too close for comfort

Overall, the doomed planet WASP-12b orbits so close to its yellow dwarf star that almost an entire year fits into a single Earth day. This proximity classifies WASP-12b as an “ultra-hot Jupiter” planet, a name that’s appropriate considering the radiation from this star incessantly surrounds the planet, giving it a surface temperature of about 4,000 degrees Fahrenheit (2,210 degrees Celsius).

However, that’s not the only thing that makes this doomed world an extreme exoplanet, unlike anything found in the solar system. The immense gravity that WASP-12b feels just 3.3 million kilometers away from its star generates such large tidal forces that it is now shaped like an egg.

This gravitational influence also removes material from WASP-12b, which forms a disk of matter around the planet’s yellow star.

When WASP-12b was discovered in 2008, it was the hottest planet ever seen, a record it surrendered to another world called Kelt-9b in 2018. At the time, WASP-12b was also the closest planet to its star, although that record is now held by K2-137b, which is just over half a million kilometers from its red dwarf star some 322 light-years away. soil has been removed. .

Although WASP-12b is just one of many hot Jupiter exoplanets discovered since the mid-1990s, something has always distinguished this planet.

WASP-12b, for example, appeared to experience variations in the time it takes to orbit its star. Previous theories had attributed this to factors such as the planet’s position relative to Earth and a gradual shift in its orbit.

Leonardi and colleagues examined WASP-12b’s timing variation by looking at 28 observations of the planet made as it crossed, or “transited,” the face of its parent star. This was done in collaboration with the Asiago Search for Transit Timing Variations of Exoplanets (TASTE) project. These observations were collected over a twelve-year period between 2010 and 2022 by the Asiago Observatory in Italy.

This study not only showed that WASP-12b’s fiery fate in about 3 million years is the result of a phenomenon called “tidal dissipation,” but it also gave the team the first clues that the planet’s yellow star is very active is. During periods of high activity, stars become covered by dark spots called sunspots and experience more extreme bursts of charged particles in the form of plasma. This means the team may have captured WASP-12b when it experienced an even more violent explosion from its star than normal.

One surprise the team’s analysis yielded was some evidence suggesting the dwarf star has already reached the end of its main sequence life, a period when stars burn hydrogen in their cores.

For low- to intermediate-mass stars such as WASP-12, which has a mass and width about 1.5 times the mass and width of the Sun, the end of hydrogen combustion in the core heralds a lifespan that is called the ‘sub-giant phase’. with the hydrogen burning moving towards the outer layers of the star.

‘According to tidal theory, the dissipation we see in the system is too strong to be explained by a main sequence star. If the star had already left the main sequence and entered its sub-giant phase, this could be easily explained.” Leonardi said. ‘To test this theory, we used high-resolution optical spectra from the High Accuracy Radial Velocity Planet Searcher in the Northern Hemisphere (HARPS-N) to infer the star’s stellar parameters and infer its evolutionary stage.

“However, according to our results, the star is still in the main sequence and has not yet entered its sub-giant stage.”

This means the team still needs to explain how rapid tidal spreading could be caused by a main sequence dwarf star.

When WASP-12b finally enters its star in about 3 million years, it will trigger changes that observers from Earth should be able to see – assuming intelligent life is still present on our planet.

“When the planet inevitably collides with the star, the first indication will be a burst of brightness, making the star hundreds of times brighter than it is now,” Leonardi said. “This increase will not last long and will disappear quickly. But perhaps the people of the future can be there to see and study it.”

The team’s research is currently available on the paper repository arXiv.

Related stories:

– New ‘warm Jupiter’ exoplanet discovered by NASA’s planet-hunting satellite

— Some exoplanets shrink. This is why

— Star blows away the atmosphere of a giant exoplanet, leaving behind a huge tail

Leonardi thinks the findings regarding WASP-12b’s doomed status could indicate that other ultra-hot Jupiters could also be on a collision course with their stars.

“We still need to figure out whether what we observed is a unique scenario or a common event in the universe,” Leonardi said. ‘According to some population studies, the number of hot Jupiters orbiting very close to their stars decreases as we observe older stars, so this could be an indication that many planets are experiencing tidal decay and colliding with their stars.’

Leonardi added that he is now working with the team behind the European Space Agency (ESA) mission characterizing ExOPlanet Satellite (CHEOPS) to determine the orbital decay rates of other hot Jupiters.

“This study is just the beginning of a long search for orbital decay,” he concluded.

The team’s research is published on the paper repository arXiv.

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