Friday, July 1, 2016
NASA ROVER'S SAND-DUNE STUDIES YIELD SURPRISE
Two sizes of ripples are evident in this Dec. 13, 2015, view of a top of a Martian sand dune
Two sizes of ripples are evident in this Dec. 13, 2015, view of a top of a Martian sand dune, from NASA's Curiosity Mars rover. Sand dunes and the smaller type of ripples also exist on Earth. The larger ripples are a type not seen on Earth nor previously recognized as a distinct type on Mars.
Credits: NASA/JPL-Caltech/MSSS
The determination that these mid-size ripples are a distinct type resulted from observations by NASA's Curiosity Mars rover. Six months ago, Curiosity made the first up-close study of active sand dunes anywhere other than Earth, at the "Bagnold Dunes" on the northwestern flank of Mars' Mount Sharp.
"Earth and Mars both have big sand dunes and small sand ripples, but on Mars, there's something in between that we don't have on Earth," said Mathieu Lapotre, a graduate student at Caltech in Pasadena, California, and science team collaborator for the Curiosity mission. He is the lead author of a report about these mid-size ripples published in the July 1 issue of the journal Science.
Both planets have true dunes -- typically larger than a football field -- with downwind faces shaped by sand avalanches, making them steeper than the upwind faces.
Earth also has smaller ripples -- appearing in rows typically less than a foot (less than 30 centimeters) apart -- that are formed by wind-carried sand grains colliding with other sand grains along the ground. Some of these "impact ripples" corrugate the surfaces of sand dunes and beaches.
Images of Martian sand dunes taken from orbit have, for years, shown ripples about 10 feet (3 meters) apart on dunes' surfaces. Until Curiosity studied the Bagnold Dunes, the interpretation was that impact ripples on Mars could be several times larger than impact ripples on Earth. Features the scale of Earth's impact ripples would go unseen at the resolution of images taken from orbit imaging and would not be expected to be present if the meter-scale ripples were impact ripples.
"As Curiosity was approaching the Bagnold Dunes, we started seeing that the crest lines of the meter-scale ripples are sinuous," Lapotre said. "That is not like impact ripples, but it is just like sand ripples that form under moving water on Earth. And we saw that superimposed on the surfaces of these larger ripples were ripples the same size and shape as impact ripples on Earth."
Besides the sinuous crests, another similarity between the mid-size ripples on Mars and underwater ripples on Earth is that, in each case, one face of each ripple is steeper than the face on the other side and has sand flows, as in a dune. Researchers conclude that the meter-scale ripples are built by Martian wind dragging sand particles the way flowing water drags sand particles on Earth -- a different mechanism than how either dunes or impact ripples form. Lapotre and co-authors call them "wind-drag ripples."
"The size of these ripples is related to the density of the fluid moving the grains, and that fluid is the Martian atmosphere," he said. "We think Mars had a thicker atmosphere in the past that might have formed smaller wind-drag ripples or even have prevented their formation altogether. Thus, the size of preserved wind-drag ripples, where found in Martian sandstones, may have recorded the thinning of the atmosphere."
The researchers checked ripple textures preserved in sandstone more than 3 billion years old at sites investigated by Curiosity and by NASA's Opportunity Mars rover. They found wind-drag ripples about the same size as modern ones on active dunes. That fits with other lines of evidence that Mars lost most of its original atmosphere early in the planet's history.
Other findings from Curiosity's work at the Bagnold Dunes point to similarities between how dunes behave on Mars and Earth.
"During our visit to the active Bagnold Dunes, you might almost forget you’re on Mars, given how similar the sand behaves in spite of the different gravity and atmosphere. But these mid-sized ripples are a reminder that those differences can surprise us," said Curiosity Project Scientist Ashwin Vasavada, of NASA's Jet Propulsion Laboratory in Pasadena.
After examining the dune field, Curiosity resumed climbing the lower portion of Mount Sharp. The mission is investigating evidence about how and when ancient environmental conditions in the area evolved from freshwater settings favorable for microbial life, if Mars has ever hosted life, into conditions drier and less habitable. For more information about Curiosity, visit:
http://mars.jpl.nasa.gov/msl
Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.webster@jpl.nasa.gov
Robert Perkins
Caltech, Pasadena, Calif.
626-395-1862 / 626-658-1053
rperkins@caltech.edu
2016-169
HUBBLE CAPTURES VIVID AURORAS IN JUPITER’S ATMOSPHERE
Astronomers are using the NASA/ESA Hubble Space Telescope to study auroras — stunning light shows in a planet’s atmosphere — on the poles of the largest planet in the solar system, Jupiter. This observation program is supported by measurements made by NASA’s Juno spacecraft, currently on its way to Jupiter.
Jupiter, the largest planet in the solar system, is best known for its colorful storms, the most famous being the Great Red Spot. Now astronomers have focused on another beautiful feature of the planet, using Hubble's ultraviolet capabilities.
Astronomers are using NASA's Hubble Space Telescope to study auroras — stunning light shows in a planet's atmosphere — on the poles of the largest planet in the solar system, Jupiter.
Credits: NASA, ESA, and J. Nichols (University of Leicester)
The extraordinary vivid glows shown in the new observations are known as auroras. They are created when high-energy particles enter a planet’s atmosphere near its magnetic poles and collide with atoms of gas. As well as producing beautiful images, this program aims to determine how various components of Jupiter’s auroras respond to different conditions in the solar wind, a stream of charged particles ejected from the sun.
This observation program is perfectly timed as NASA’s Juno spacecraft is currently in the solar wind near Jupiter and will enter the orbit of the planet in early July 2016. While Hubble is observing and measuring the auroras on Jupiter, Juno is measuring the properties of the solar wind itself; a perfect collaboration between a telescope and a space probe.
“These auroras are very dramatic and among the most active I have ever seen”, said Jonathan Nichols from the University of Leicester, U.K., and principal investigator of the study. “It almost seems as if Jupiter is throwing a firework party for the imminent arrival of Juno.”
To highlight changes in the auroras Hubble is observing Jupiter almost daily for several months. Using this series of far-ultraviolet images from Hubble's Space Telescope Imaging Spectrograph, it is possible for scientists to create videos that demonstrate the movement of the vivid auroras, which cover areas bigger than Earth.
Not only are the auroras huge in size, they are also hundreds of times more energetic than auroras on Earth. And, unlike those on Earth, they never cease. While on Earth the most intense auroras are caused by solar storms — when charged particles rain down on the upper atmosphere, excite gases and cause them to glow red, green and purple — Jupiter has an additional source for its auroras.
The strong magnetic field of the gas giant grabs charged particles from its surroundings. This includes not only the charged particles within the solar wind but also the particles thrown into space by its orbiting moon Io, known for its numerous and large volcanoes.
The new observations and measurements made with Hubble and Juno will help to better understand how the sun and other sources influence auroras. While the observations with Hubble are still ongoing and the analysis of the data will take several more months, the first images and videos are already available and show the auroras on Jupiter’s north pole in their full beauty.
The Jet Propulsion Laboratory (JPL) in Pasadena, California, manages the Juno mission for Southwest Research Institute in San Antonio, Texas. Juno is part of NASA's New Frontiers Program, which is managed at NASA's Marshall Space Flight Center in Huntsville, Alabama, for NASA's Science Mission Directorate in Washington, D.C. Lockheed Martin Space Systems, Denver, built the spacecraft. The California Institute of Technology in Pasadena manages JPL for NASA.
The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy (AURA) in Washington, D.C.
For images, video and more information about auroras on Jupiter and Hubble, visit:
http://hubblesite.org/news/2016/24
http://www.nasa.gov/hubble
European Space Agency
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