Science Pictures of the Week: Mars scars unexpectedly darken, Saturn's shorter day and looking down on the aurora
Sunday, March 29, 2015, 5:50 PM - The (mostly) fading scars of Curiosity's landing, Saturn's day gets shorter, and a new look at the St. Patrick's Day geomagnetic storm. It's Science Pictures of the Week!
Time heals all wounds, even on Mars (well, mostly)
When NASA's Curiosity rover landed on Mars on August 6, 2012, its descent stage gently lowered it to the surface by a sky crane, and then rocketed off to slam into the ground. The impact of the descent stage produced a blast 'scar', revealing the darker Martian rock that lay underneath the brighter dust. In the time since then, this scar had been 'healing' over, but then it unexpectedly darkened again.
According to NASA JPL's website:
"Spacecraft like Curiosity create these dark blast zone patterns where bright dust is blown away by the landing," said Ingrid Daubar, a HiRISE team scientist at NASA's Jet Propulsion Laboratory, Pasadena, California, who has used similar blast zones to find fresh meteor impact sites on Mars. "We expected to see them fade as the wind moved the dust around during the months and years after landing, but we've been surprised to see that the rate of change doesn't appear to be consistent."
One purpose for repeated follow-up imaging of Curiosity's landing area has been to check whether scientists could model the fading and predict how long it would take for the scars to disappear. Daubar's work on this aids preparations for NASA's next Mars lander, InSight, on track for launch in March 2016. The InSight mission will deploy a heat probe that will hammer itself a few yards, or meters, deep into the ground to monitor heat coming from the interior of the planet. The brightness of the ground affects temperature below ground, because a dark surface warms in sunshine more than a bright one does.
For more animations, showing how the other results of Curiosity's landing have changed over time, follow this link to the JPL website.
Saturn's day gets shorter
Knowing the length of a day on a planet is an important bit of its basic information, and it can tell scientists a lot about the planet's physical properties and characteristics. But what if you can't see the surface of the planet, or the planet doesn't technically have a surface (at least not one that we have any way to access)? This is the problem that scientists have been running into for gas giant planets like Saturn for years.
According to researchers at Tel Aviv University and the Weizmann Institute of Science:
For years, scientists have had difficulty coming up with a precise measurement of Saturn's rotation. "In the last two decades, the standard rotation period of Saturn was accepted as that measured by Voyager 2 in the 1980s: 10 hours, 39 minutes, and 22 seconds," said Dr. Helled. "But when the Cassini spacecraft arrived at Saturn 30 years later, the rotation period was measured as eight minutes longer. It was then understood that Saturn's rotation period could not be inferred from the fluctuations in radio radiation measurements linked to Saturn's magnetic field, and was in fact still unknown." The Cassini spacecraft had measured a signal linked to Saturn's magnetic field with a periodicity of 10 hours, 47 minutes and 6 seconds long - slower than previous recordings.
"Since then, there has been this big open question concerning Saturn's rotation period," said Dr. Helled. "In the last few years, there have been different theoretical attempts to pin down an answer. We came up with an answer based on the shape and gravitational field of the planet. We were able to look at the big picture, and harness the physical properties of the planet to determine its rotational period."
The new length of Saturn's day? According to readings of the planet's shape and magnetic field, the researchers determined that it's 10 hours, 32 minutes and 45 seconds (give or take about a half-second).
Looking down on the Northern Lights
On March 17, the edge of an expanding blast of solar matter swept past Earth, impacting on the planet's magnetic field and sparking off the most intense geomagnetic storm in the past decade. How far south did the Northern Lights reach that night? This view from space gives a good indication.
According to the NASA Earth Observatory website:
On Sunday, March 15, a coronal mass ejection exploded off the Sun towards Earth, as observed by NASA and National Oceanic and Atmospheric Administration (NOAA) instruments. By March 17, the burst of solar particles and energy reached Earth and kept the solar wind stream at potent levels for more than 24 hours. The storm reached a G4 or “severe” level on NOAA’s geomagnetic storm scale, and the Kp index—a metric for global geomagnetic storm activity—fluctuated between 6 to 8 on a scale that goes to 9. The “northern lights” reached as far south as the central and southern United States.
Using the “day-night band” (DNB) of the Visible Infrared Imaging Radiometer Suite (VIIRS), the Suomi NPP satellite acquired this view (above) of the aurora borealis around 1:30 a.m. Eastern Daylight Time on March 18, 2015. Auroras appear as white streaks over Hudson Bay, southern Canada, and the northern United States. The DNB sensor detects dim light signals such as auroras, airglow, gas flares, city lights, and reflected moonlight. In the image above, the sensor detected visible light emissions as energetic particles rained down from Earth’s magnetosphere into the gases of the upper atmosphere.