[Left] — This is a Hubble Space Telescope near-infrared-light image of a brown dwarf located 170 light-years away from Earth. The object is no more than 30 times the mass of Jupiter, making it too small to sustain nuclear fusion to shine as a star.
[Right] — When the glow of the brown dwarf is subtracted from the image, a smaller and fainter companion object becomes visible. No more that four times the mass of Jupiter, this companion is dubbed a "super-Jupiter." It has an estimated diameter as big as 40 percent greater than Jupiter's diameter. The world is 5 billion miles from the brown dwarf, nearly twice the distance between our sun and the planet Neptune.
Because the planet is only 10 million years old, it is so hot it may
rain molten glass and iron in its atmosphere. Hubble has measured
fluctuations in the planet's brightness that suggests the planet has
patchy clouds as it completes one rotation every 10 hours.Credit: NASA, ESA, and Y. Zhou (University of Arizona)
This graph plots small changes in the infrared brightness of a
super-Jupiter as measured by the Hubble Space Telescope. The S-shaped
curve is extrapolated from the data points. Its sinusoidal shape
suggests that brightness changes are a result of a 10-hour rotation
period (horizontal axis). The vertical axis shows small changes in
brightness. This would mean that the planet likely has patchy clouds
that influence the amount of infrared radiation observed as the planet
rotates. At a distance of 170 light-years from Earth, the planet is too
far away for Hubble to actually resolve atmospheric structure. Credit: NASA, ESA, Y. Zhou (University of Arizona), and P. Jeffries (STScI)
Astronomers using NASA's Hubble Space Telescope have measured the rotation rate of an extreme exoplanet by observing the varied brightness in its atmosphere. This is the first measurement of the rotation of a massive exoplanet using direct imaging.
"The result is very exciting," said Daniel Apai of the University of
Arizona in Tucson, leader of the Hubble investigation. "It gives us a
unique technique to explore the atmospheres of exoplanets and to
measure their rotation rates."
The planet, called 2M1207b, is about four times more massive than
Jupiter and is dubbed a "super-Jupiter." It is a companion to a failed
star known as a brown dwarf, orbiting the object at a distance of 5
billion miles. By contrast, Jupiter is approximately 500 million miles
from the sun. The brown dwarf is known as 2M1207. The system resides
170 light-years away from Earth.
Hubble's image stability, high resolution, and high-contrast imaging
capabilities allowed astronomers to precisely measure the planet's
brightness changes as it spins. The researchers attribute the
brightness variation to complex clouds patterns in the planet's
atmosphere. The new Hubble measurements not only verify the presence of
these clouds, but also show that the cloud layers are patchy and
colorless.
Astronomers first observed the massive exoplanet 10 years ago with
Hubble. The observations revealed that the exoplanet's atmosphere is
hot enough to have "rain" clouds made of silicates: vaporized rock that
cools down to form tiny particles with sizes similar to those in
cigarette smoke. Deeper into the atmosphere, iron droplets are forming
and falling like rain, eventually evaporating as they enter the lower
levels of the atmosphere.
"So at higher altitudes it rains glass, and at lower altitudes it
rains iron," said Yifan Zhou of the University of Arizona, lead author
on the research paper. "The atmospheric temperatures are between about
2,200 to 2,600 degrees Fahrenheit."
The super-Jupiter is so hot that it appears brightest in infrared
light. Astronomers used Hubble's Wide Field Camera 3 to analyze the
exoplanet in infrared light to explore the object's cloud cover and
measure its rotation rate. The planet is hot because it is only about
10 million years old and is still contracting and cooling. For
comparison, Jupiter in our solar system is about 4.5 billion years old.
The planet, however, will not maintain these sizzling temperatures.
Over the next few billion years, the object will cool and fade
dramatically. As its temperature decreases, the iron and silicate
clouds will also form lower and lower in the atmosphere and will
eventually disappear from view.
Zhou and his team have also determined that the super-Jupiter
completes one rotation approximately every 10 hours, spinning at about
the same fast rate as Jupiter.
This super-Jupiter is only about five to seven times less massive
than its brown-dwarf host. By contrast, our sun is about 1,000 times
more massive than Jupiter. "So this is a very good clue that the 2M1207
system we studied formed differently than our own solar system," Zhou
explained. The planets orbiting our sun formed inside a circumstellar
disk through accretion. But the super-Jupiter and its companion may
have formed throughout the gravitational collapse of a pair of separate
disks.
"Our study demonstrates that Hubble and its successor, NASA's James
Webb Space Telescope, will be able to derive cloud maps for exoplanets,
based on the light we receive from them," Apai said.
Indeed, this
super-Jupiter is an ideal target for the Webb telescope, an infrared
space observatory scheduled to launch in 2018. Webb will help
astronomers better determine the exoplanet's atmospheric composition
and derive detailed maps from brightness changes with the new technique
demonstrated with the Hubble observations.
Results from this study will appear in the Feb. 18, 2016, edition of The Astrophysical Journal.
Contact:
Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Source: HubbleSite
