Skywatchers across the United States will get to enjoy a total lunar eclipse Sunday, Sept. 27.
“Don’t tell me what it was designed to do. Tell me what it can do!”
That line was uttered in the movie “Apollo 13,” but could also be applied to the daring eclipse observations that NASA’s Lunar Reconnaissance Orbiter will do of the moon’s surface on Sunday.
Sunday’s eclipse is special as it follows three other total lunar eclipses in the past 18 months (usually you don’t get that many in a row) and the moon will be at its closest point in its orbit to Earth, making it slightly bigger in the sky than usual — an event popularly known as a “Supermoon.”
The LRO has been observing Earth’s satellite since 2009, and wasn’t designed to operate during eclipses. The solar-powered spacecraft would switch off almost everything until sunlight returned again. But as controllers became experienced with the drops in power during LRO’s time in shadow, they got comfortable enough to turn on one instrument: the Diviner.
More formally known as the Diviner Lunar Radiometer Experiment, the instrument looks at day-night changes in temperature on the moon. And it turns out that during an eclipse, the plunge in temperature is sudden — almost like leaving a hot tub for an icy pool, according to NASA. Click here to watch a NASA animation of what it looks like, from the surface of the moon, during a lunar eclipse.
“Ideally we want to measure the full range of temperature variation during the eclipse,” Noah Petro, the deputy project scientist for LRO, told Discovery News. Petro is based at the NASA Goddard Space Flight Center in Maryland.
For most past eclipses, the polar-orbiting spacecraft has been limited to viewing the terminator — the day-night line — where the surface is cool to begin with. This time, the spacecraft will zoom over an area that is more the equivalent of 9 a.m. sunlight on Earth — mid-morning, offering a better sense of how much the temperature changes during an eclipse.
“Most recent (eclipses) have been good, but this will be the sweet spot and the last eclipse for a number of years — not until 2018,” Petro added.
From the past eclipse data, the researchers have seen substantial swings in temperature in a couple of hours — several hundred degrees Fahrenheit — in the soil, particularly in the upper two centimeters. (They can’t see into the soil, but can model it.)
How the Sept. 27, 2015 lunar eclipse will take place.NASA
Diviner can sense temperature as deep as 15 centimeters into the lunar soil. Down below that first layer, the soil stays warmer, meaning that top 2 cm must act as a sort of insulator. Models suggest that it’s because the regolith (lunar soil) has space in between the grains.
With each subsequent eclipse, scientists have answered different questions depending on what terrain was underneath, Benjamin Greenhagen, the deputy principal investigator for Diviner, told Discovery News. Previously they were looking at rocky craters (to see the depth of dust over the rocks) and investigated a magnetic anomaly.
“This time, we’ll go over a couple of different areas,” said Greenhagen, who is based at Maryland’s Johns Hopkins University Applied Physics Laboratory. “We’ll look at two large pyroclastic deposits — these are massive volcanic eruptions, with lots of volcanic glass and small particles. We’ll also go over an area with small rocks … (and) try to characterize the rocks.”
After the eclipse is done, scientists will take the data from several of these events and combine them to get a picture of how the top layer of soil behaves. There also will be careful monitoring of LRO’s health to make sure the battery behaves as expected, but no problems are anticipated at this time, Petro said.