Skip to main content

Hubble watches an extreme exoplanet being stripped by its star

Of the many strange exoplanets discovered to date, one of the most extreme has to be a world called AU Mic b. This Neptune-sized planet orbits close enough to its star that a year there lasts just over a week, and it is bombarded by dramatic flares from its host star which cook the planet with radiation.

Recently, Hubble observed this system to learn more about the relationship between the exoplanet and its star, technically called AU Microscopii.  The planet’s hydrogen atmosphere is blown away by radiation from the star, but there were confusing findings that seemed to show that no atmosphere was being lost at some times, but significant amounts of atmosphere were lost at other times.

This artist's illustration shows a planet (dark silhouette) passing in front of the red dwarf star AU Microscopii.
This artist’s illustration shows a planet (dark silhouette) passing in front of the red dwarf star AU Microscopii. The planet is so close to the eruptive star a ferocious blast of stellar wind and blistering ultraviolet radiation is heating the planet’s hydrogen atmosphere, causing it to escape into space. Four times Earth’s diameter, the planet is slowly evaporating its atmosphere, which stretches out linearly along its orbital path. This process may eventually leave behind a rocky core. The illustration is based on measurements made by the Hubble Space Telescope. NASA, ESA, Joseph Olmsted (STScI)

“We’ve never seen atmospheric escape go from completely not detectable to very detectable over such a short period when a planet passes in front of its star,” said lead researcher Keighley Rockcliffe of Dartmouth College in a statement. “We were really expecting something very predictable, repeatable. But it turned out to be weird. When I first saw this, I thought ‘That can’t be right.'”

This strange variability could be due to changes in the flares given off by the star. The star is very young to host planets, at less than 100 million years old, and its flares are caused by the interaction of magnetic fields and the stellar atmosphere. This creates an extreme stellar wind effect which blows away the atmosphere of the nearby planet.

The researchers suggest that the strange variation in the planet’s atmospheric loss could be due to a particularly strong solar flare occurring shortly before Hubble took its measurements which could have ionized the hydrogen coming off the planet, making it invisible to Hubble’s instruments. Or it could be that the stellar winds do actually cause the atmospheric loss to vary considerably.

The researchers are interested in learning about how exoplanets fare in extreme radiation environments like this one.

“We want to find out what kinds of planets can survive these environments. What will they finally look like when the star settles down? And would there be any chance of habitability eventually, or will they wind up just being scorched planets?” said Rockcliffe. “Do they eventually lose most of their atmospheres and their surviving cores become super-Earths? We don’t really know what those final compositions look like because we don’t have anything like that in our solar system.”

The research is published in The Astronomical Journal.

Editors' Recommendations

Georgina Torbet
Georgina is the Digital Trends space writer, covering human space exploration, planetary science, and cosmology. She…
First indications of a rare, rainbow ‘glory effect’ on hellish exoplanet
For the first time, potential signs of the rainbow-like ‘glory effect’ have been detected on a planet outside our Solar System. Glory are colourful concentric rings of light that occur only under peculiar conditions. Data from ESA’s sensitive Characterising ExOplanet Satellite, Cheops, along with several other ESA and NASA missions, suggest this delicate phenomenon is beaming straight at Earth from the hellish atmosphere of ultra-hot gas giant WASP-76b, 637 light-years away.

Just from looking at our own solar system, we can see that planets come in a wide variety of colors -- from the dusty red of Mars to the bright blues of Uranus and Neptune. Planets like Jupiter have beautiful bands of color caused by variations in the atmosphere, while it's hard to even see the surface of Venus because its atmosphere is so thick. But there are other variations in color which planets can display, like a stunning rainbow-hued set of circular rings called a glory.

Glories are observed on Earth, and have been seen just once on another planet, Venus. But now, researchers believe they may have identified a glory on a planet outside our solar system for the first time. The extreme exoplanet WASP-76b could be host to the first known extrasolar glory, observed by the European Space Agency (ESA)'s Characterising ExOplanet Satellite (Cheops).

Read more
Hubble captures the dramatic jets of a baby star
FS Tau is a multi-star system made up of FS Tau A, the bright star-like object near the middle of the image, and FS Tau B (Haro 6-5B), the bright object to the far right that is partially obscured by a dark, vertical lane of dust. The young objects are surrounded by softly illuminated gas and dust of this stellar nursery. The system is only about 2.8 million years old, very young for a star system. Our Sun, by contrast, is about 4.6 billion years old.

A new image from the Hubble Space Telescope shows the drama that unfolds as a new star is born. Within a swirling cloud of dust and gas, a newly formed star is giving off powerful jets that blast away material and cut through the nearby dust of the surrounding nebula to create this stunning vista.

The image shows a system called FS Tau, located 450 light-years away in a region called Taurus-Auriga. Within this region are many stellar nurseries with new stars forming, making it a favorite target for astronomers studying star formation. But this particular system stands out for the dramatic nature of its newborn star, which has formed an epic structure called a Herbig-Haro object.

Read more
Hubble images the spooky Spider Galaxy
This image from the NASA/ESA Hubble Space Telescope shows the irregular galaxy UGC 5829.

This week's image from the Hubble Space Telescope shows an irregular galaxy, the spindly arms and clawed shape of which has led to it being named the Spider Galaxy. Located 30 million light-years away, the galaxy also known as UGC 5829 is an irregular galaxy that lacks the clear, orderly arms seen in spiral galaxies like the Milky Way.

This image from the NASA/ESA Hubble Space Telescope shows the irregular galaxy UGC 5829. ESA/Hubble & NASA, R. Tully, M. Messa

Read more