NASA announced Monday that scientists using the Hubble Space Telescope have found evidence of water plumes on Europa, which means that spacecraft may be able to explore the moon’s ocean without the need to penetrate its icy surface.
A research team led by astronomer William Sparks of the Space Telescope Science Institute in Baltimore used a technique that has often been instrumental in discovering exoplanets to identify the plumes.
As an exoplanet moves in front of its star, the light from that star changes as it passes through the exoplanet’s atmosphere. This happens because the light encounters a variety of molecules.
On Europa, Sparks and his team noticed that the molecules in the moon’s atmosphere included water vapor. That led them to embark on a quest to determine whether water from Europa’s subsurface ocean is being expelled into space.
The scientists observed Europa pass in front of Jupiter, from which the Sun’s light would be reflected through the atmosphere of the Jovian moon, ten times in 15 months. On three of the occasions water vapor was detected.
“This is an exciting find because it potentially gives us access to the ocean below,” Sparks said at a NASA teleconference on Monday.
Scientists are interested in sampling Europa’s ocean because it may provide indications of whether the moon is, or ever has been, hospitable to life.
“On Earth, life is found wherever there is energy, water, and nutrients, so we have a special interest in any place that has those characteristics,” Dr. Paul Hertz, director of NASA’s astrophysics division in Washington, D.C., said. “Europa might be such a place.”
Europa has a large sub-surface ocean that is thought to contain more water than all of the oceans on Earth. However, the satellite also has a thick icy crust atop that ocean.
The water plumes may rise as high as 200 kilometers off Europa’s surface.
“Europa’s ocean is considered to be one of the most promising places that could potentially harbor life in the solar system,” Geoff Yoder, the acting associate administrator for NASA’s Science Mission Directorate, said. “These plumes, if they do indeed exist, may provide another way to sample Europa’s subsurface.”
A team led by Lorenz Roth of the Southwest Research Institute in Austin, Tex. identified water plumes rising from Europa’s south pole once during 2012.
The Roth group used the Hubble Space Telescope’s Imaging Spectrograph to identify hydrogen and oxygen ions by the ultraviolet radiation they emit after particles accelerated by Jupiter’s magnetic field split water molecules in the Europan atmosphere.
The STScI group also used the STIS instrument, but instead obtained imagery of Europa’s atmosphere in ultraviolet light.
“It’s a technique that complements the Roth team’s,” Dr. Jennifer J. Wiseman, an astrophysicist at NASA’s Goddard Space Flight Center and the agency’s senior scientist assigned to the Hubble Space Telescope, said.
Wiseman explained that STIS’ ultraviolet imaging capacity was particularly helpful to the STScI researchers.
“In ultraviolet light, the surface of Jupiter looks more uniform in color than in visible light, so that allowed the Sparks team to more clearly see the silhouette image of the possible plumes on Europa as the moon passed in front of the smooth Jupiter background,” she wrote in an email message.
The Roth team also used STIS during their quest for Europa’s plumes in 2012.
Sparks said that, notwithstanding a different methodology of investigation, the STScI results are similar to those found by Roth and his colleagues.
“When we calculate in a completely different way the amount of material that would be needed to create these absorption features, it’s pretty similar to what Roth and his team found,” he explained. “The estimates for the mass are similar, the estimates for the height of the plumes are similar. The latitude of two of the plume candidates we see corresponds to their earlier work.”
The STScI and Roth teams have not seen plumes erupting from Europa at the same times. Sparks and his colleagues observed what they believe to be water plumes in January, March, and April, 2014.
Wiseman said that detection of Europa’s plumes is difficult.
“Such plumes would be faint, probably intermittent, and the ultraviolet wavelengths of light being observed are at the high frequency edge of what Hubble can detect,” she wrote in an email message.
Sparks explained that he and his team do not claim that their work proves the plumes’ existence, though he also said Monday that he does not believe that any other explanation for the findings his team made is likely.
“In a formal sense, we have a statistically significant result,” Sparks said. “The problem is that there may be something we don’t understand about the instrument or the scene. It’s more of a subjective uncertainty than a quantitative uncertainty.”
“I’m not aware of any other plausible natural explanation for the appearance of these patches of absorption,” he continued.
Two of the water plumes that were apparently observed by Sparks and his team occurred near the south pole of Europa and one was seen near the moon’s equator.
A paper detailing the findings by the STScI team will be published in the Sept. 29 edition of Astrophysical Journal.
Saturn’s moon Enceladus is the only body in the solar system known to eject water vapor to space.
Wiseman said during Monday’s teleconference that NASA plans to use the James Webb Space Telescope, due to be launched in 2018, to further investigate the possible water plumes of Europa.
NOTE 1: This post was updated at 5:38 pm MDT on Sept. 27, 2016 to add a discussion of Dr. Jennifer Wiseman’s interview responses.
NOTE 2: This post was updated at 9:32 pm MDT on Sept. 27, 2016 to correct an inaccurate statement contained in the headline, correct several minor errors in the quotation of Dr. Jennifer Wiseman’s email communication, and correct the acronym applicable to the Space Telescope Science Institute.
NOTE 3: This post was updated at 9:37 pm MDT on Sept. 27, 2016 to clarify the difference between the Roth team’s use of the Hubble Space Telescope’s Imaging Spectrograph in 2012 and the STScI team’s use of that instrument in 2014.
A private company succeeded Friday in landing a rocket upright at sea for the first time in history.
SpaceX, which handles cargo launches for the International Space Station, said on its Twitter feed that the first stage of a Falcon 9 rocket that had lifted the Dragon cargo capsule to orbit had landed on a floating barge.
The company posted a video of the landing on its Twitter feed.
President Obama congratulated SpaceX in a message posted to his official Twitter feed, as did NASA.
Tim Kopra, a NASA astronaut on board the International Space Station, posted to his Twitter account Friday a photo of the moon. The photo is worthy of a share:
NASA has released an image obtained by the New Horizons spacecraft that appears to show a frozen lake on Pluto.
The photograph is of a mountainous area north of Sputnik Planum and shows details as small as 130 meters in size.
The substance in the lake is not water. It is instead, in all likelihood, frozen nitrogen. If you look closely, you can also see features around the lake that may have once carried liquids.
Pluto must have had a thicker atmosphere that exerted greater pressure and conditions on the dwarf planet’s surface must have been warmer in the past if liquids flowed there.
NASA released the image on March 24.
An American astronaut has come home after spending 340 days in space.
Scott Kelly arrived in Houston today aboard a small aircraft after a Russian Soyuz spacecraft brought him and several other crewmembers from the International Space Station back to the planet’s surface yesterday.
The purpose of Kelly’s long stay in space was to examine the impacts of a low gravity environment on human health. NASA used Kelly’s Earth-bound twin brother, Mark Kelly, as a control.
During his American record-breaking stay in space, Kelly posted numerous spectacular images of Earth and space. This one is from this year’s “leap day,” Feb. 29:
Kelly saw 10,944 sunrises and sunsets during his 11-plus months aboard the ISS.
Of course, Kelly’s mission was not all about photography and videography. He also participated in efforts to grow flowers and plants aboard the ISS, an experiment aimed at assessing the viability of producing food while on the way to and from Mars.
During his time in space Kelly’s rate of aging slowed. Astrophysicist Neil DeGrasse Tyson made that point in a tweet posted Wednesday:
Kelly, 52, has been an astronaut for nearly 20 years and is a veteran of two space shuttle flights and several expeditions to the ISS.
A retired U.S. Navy captain, Kelly is also a highly experienced pilot. According to his official NASA biography, Kelly has flown over 8,000 hours in more than 40 different aircraft. Those included two combat aircraft: the F-14 Tomcat and the F/A-18 Hornet. He has landed an airplane on the deck of an aircraft carrier more than 250 times.
Kelly’s twin brother, Mark Kelly, is also a retired naval officer and former astronaut. Mark Kelly is the husband of former U.S. representative Gabrielle Giffords, who was the victim of an assassination attempt in 2011.
NASA’s Cassini spacecraft made its last fly-by of Enceladus on Dec. 19. Since then it has been transmitting to Earth images taken of the ocean moon, including this beauty received Feb. 15:
As NASA’s Cassini probe continues its exploration of Saturn and its moons, it sends home some amazing images of that distant region of our solar system.
Yesterday, NASA released an image showing three of the gas giant’s moons: Tethys, Enceladus, and Mimas. Here it is:
According to NASA:
The view was acquired at a distance of approximately 837,000 miles (1.35 million kilometers) from Enceladus, with an image scale of 5 miles (8 kilometers) per pixel. Tethys was approximately 1.2 million miles (1.9 million kilometers) away with an image scale of 7 miles (11 kilometers) per pixel. Mimas was approximately 1.1 million miles (1.7 million kilometers) away with an image scale of 6 miles (10 kilometers) per pixel.
Tethys’ diameter is about 1,066 kilometers. The cratered moon orbits Saturn from a distance of about 294,600 kilometers. That is about 20 percent farther from Saturn than the Moon is from Earth. Tethys is slightly less dense than liquid water, which suggests that its structure is mostly ice. This frigid moon is tidally locked to Saturn – it does not rotate and only one side of Tethys faces Saturn.
Enceladus is smaller than Tethys, with a diameter of about 500 kilometers. The host of a sub-surface liquid water ocean, Enceladus is covered by water ice and reflects nearly all the sunlight that hits it. That makes it a very cold satellite. The surface temperature on the moon is about -201 degrees Celsius. It orbits Saturn from a mean distance of about 238,000 kilometers, which is about the same distance as Earth’s satellite is from our planet.
Mimas is the smallest of Saturn’s major moons. It is heavily cratered, with a giant crater called Herschel stretching across about one-third of its surface. That feature has led Mimas to sometimes be called the “Death Star moon” because it evokes the fictional planet-destroying spacecraft in the Star Wars films. Mimas’ diameter is about 400 kilometers; it orbits Saturn from a mean distance of about 200,000 kilometers.