Written by George McGinn
Cosmology and Space Research
September 27, 2016 at 4:32pm EST
In one of the most promising places in the Solar System where life may exist, astronomers using NASA’s Hubble Space Telescope have photographed what appears to be water vapor plumes escaping Jupiter’s moon Europa.
The team from the Space Telescope Science Institute (STScI) in Baltimore saw finger-like projections when viewing Europa as it past in front of Jupiter, according to team leader William Sparks.
The discovery occurred by accident as the team’s original proposal was to observe Europa to determine if it had an atmosphere or exosphere.
An exosphere of neon was detected on Earth’s Moon on August 17, 2015 based on study the data from the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft.
The exosphere on Earth is the last layer of our atmosphere, sitting a top of the thermosphere about 600 km (323 miles) from the Earth’s surface. It is made up of the lightest atmospheric gasses. On Earth, Hydrogen is found throughout the exosphere, including some helium, carbon dioxide and near the base at the boundary with the thermosphere, atomic oxygen.
Exospheres have been discovered on other moons of Jupiter that have a less dense lower atmosphere.
“The atmosphere of an extrasolar planet blocks some of the starlight that is behind it,” Sparks explained. “If there is a thin atmosphere around Europa, it has the potential to block some of the light of Jupiter, and we could see it as a silhouette. And so we were looking for absorption features around the limb of Europa as it transited the smooth face of Jupiter.”
This discovery has major impacts on the question of how to collect water samples.
NASA’s Hubble Space Telescope took direct ultraviolet images of the icy moon Europa transiting across the disk of Jupiter. Out of 10 observations, Hubble saw what may be water vapor plumes on three of the images. This adds another piece of supporting evidence to the existence of water vapor plumes on Europa; Hubble also detected spectroscopic signatures of water vapor in 2012. Credits: Goddard/Katrina Jackson
Until now, scientists and engineers believed that they needed to drill down through the thick ice crust of Europa before hitting H2O in liquid form. Now, NASA is thinking that they only need to collect the liquid water from one of these plumes.
Geoff Yoder, acting associate administrator for NASA’s Science Mission Directorate in Washington is one of these believers.
“These plumes, if they do indeed exist, may provide another way to sample Europa’s subsurface,” Yoder said.
It is estimated that these plumes rise to about 200 kilometers (125 miles), and it’s presumed that the water falls back down onto Europa’s surface.
This discovery also provides supporting evidence of a discovery in 2012 by a team led by Lorenz Roth of the Southwest Research Institute in San Antonio.
Roth’s team detected similar water vapors erupting from the southern polar region. The plumes he observed, while also using the Hubble Space Telescope, reached more than 160 kilometers (100 miles) into space. The San Antonio team, while using the same imaging spectrograph instrument as Sparks used, each team used different methods to arrive at the same conclusion.
To date, the two teams have not detected the plumes simultaneously, and observations suggest the plumes may sporadically erupt for a time and then stop. The two teams observed Europa a week apart resulted in Sparks’ team detecting an eruption where Roth’s team failed to find any plumes.
If these water plumes are confirmed, Europa would be the second moon in the Solar System to have them. In 2005, the Cassini orbiter detected jets of water vapor and dust coming from Saturn’s moon Enceladus.
“Hubble’s unique capabilities enabled it to capture these plumes, once again demonstrating Hubble’s ability to make observations it was never designed to make,” said Paul Hertz, director of the Astrophysics Division at NASA Headquarters in Washington. “This observation opens up a world of possibilities, and we look forward to future missions — such as the James Webb Space Telescope — to follow up on this exciting discovery.”
After the 2018 launch of NASA’s James Webb Space Telescope, scientist can use its infrared vision to confirm venting or plumes on Europa.
The work by Sparks and his colleagues will be published in the Sept. 29 issue of the Astrophysical Journal.