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.
The amount of summer sea ice in the Arctic fell this year to the second-lowest ever recorded by satellite.
NASA and the National Snow and Ice Data Center in Boulder, Colo. announced Thursday that the Arctic has reached its summer season low extent.
The 4.14 million square kilometers of ice measured on Sept. 10 is statistically tied with the minimum ice extent during the summer of 2007 for second place on the historic minimum list. This year’s minimum ice cover is more than two million square kilometers below the 1981-2010 mean.
Arctic Summer Minimum Sea Ice Extent Record, 2007-2016
|YEAR||EXTENT (millions of km2)||DATE MEASURED|
|1979-2000 mean||6.70||Sept. 13|
|1981-2010 mean||6.22||Sept. 15|
A statement released by NSIDC starkly described the conditions in the Arctic this summer:
“This year’s minimum extent is 750,000 square kilometers (290,000 square miles) above the record low set in 2012 and is well below the two standard deviation range for the 37-year satellite record.”
Cloudy skies and atmospheric pressure conditions slowed ice melt in June and July, which may have prevented this season from becoming the most ice-free summer ever observed from space.
“June and July are usually key months for melt because that’s when you have 24 hours a day of sunlight – and this year we lost melt momentum during those two months,” Walt Meier, a scientist at NASA’s Goddard Space Flight Center, said in a statement.
The pace of melting accelerated in August when two cyclones crossed the Arctic Ocean.
Meier explained that these may have especially impacted the speed with which ice in the Chukchi and Beaufort seas melted.
The three-and-one-half decade long satellite record shows a marked decline in the mean extent of Arctic sea ice during each month of the year.
In fact, a paper published on Sept. 15 in the journal Remote Sensing of Environment concluded that no record for maximum Arctic sea ice extent has been set since 1986, while during the 37 years of satellite monitoring there have been 75 new minimum ice extent records set.
“The record makes it clear that the ice is not rebounding to where it used to be, even in the midst of winter,” Claire Parkinson, the lead author of that study and a senior climate scientist at GSFC, said.
Arctic sea ice ordinarily reaches its maximum reach for the year in March, late in the winter. The sun is not visible in the region during the winter and does not contribute much to warming of land and sea surfaces during that season.
NSIDC’s statement cautioned that the estimate released Thursday could be revised if late-summer winds or other factors causing ice melt impact the sea ice cover during the remaining days of summer.
The monitoring record dates to 1978.
Earth’s poles are the two regions of the planet that are most sensitive to warming of the atmosphere. As sea ice melts, more solar energy is absorbed by the Arctic Ocean. The deep and dark waters absorb about 90 percent of the sun’s energy that reaches them.
By contrast, expansion of sea ice during the colder autumn and winter months causes about 80 percent of the solar energy that hits the frozen surface of the region’s marine environment to be reflected to space.
August 2016 was the warmest month in recorded history, tying July 2016 for that distinction.
NASA said Monday that the mean worldwide temperature during August was 0.16 degrees Celsius hotter than the previous record-setting August and 0.98 degrees Celsius hotter than the average August between 1951-1980.
According to analysis completed by the agency’s Goddard Institute for Space Studies, August 2016 was the eleventh month in a row to reach a new high for that month’s average worldwide temperature.
IUCN warns at Hawaii conservation meeting that four of six great ape species are at high risk of extinction
The International Union for Conservation of Nature added the Eastern lowland gorilla (Gorilla berengei) to its list of critically endangered species Sunday, raising the number of great ape species that are on very cusp of extinction to four.
The three other critically endangered species of great apes are the Western gorilla (Gorilla gorilla), Bornean orangutan (Pongo pygmaeus), and Sumatran orangutan (Pongo abelii).
There are six species of great apes. The other two species – the chimpanzee (Pan troglodytes) and the bonobo (Pan paniscus) – are endangered.
G. berengei includes two subspecies. One of them, Grauer’s gorilla (G.b. graueri), has experienced a decline in population of nearly 80 percent since 1994. There are about 3,800 individuals left. The other, the Mountain gorilla (G.b. beringei), has a population of about 880 individuals.
“To see the Eastern gorilla – one of our closest cousins – slide towards extinction is truly distressing,” Inger Anderson, IUCN’s director general, said in a statement. “We live in a time of tremendous change and each IUCN Red List update makes us realize just how quickly the global extinction crisis is escalating.”
The great apes are man’s closest relatives in the natural world.
Chimpanzees and bonobos share about 98.8 percent of the human genome. Gorilla genes are about 98.4 percent identical to humans, while the orangutan genome is about 97 percent identical to man.
The IUCN announcement came at its annual conservation congress, a gathering of political leaders, conservationists, and others, in Honolulu, Hawaii.