Featured Research

from universities, journals, and other organizations

NASA missions let scientists see moon's dancing tide from orbit

Date:
May 29, 2014
Source:
NASA/Goddard Space Flight Center
Summary:
Scientists combined observations from two NASA missions to check out the moon's lopsided shape and how it changes under Earth's sway -- a response not seen from orbit before. The lopsided shape of the moon is one result of its gravitational tug-of-war with Earth. The mutual pulling of the two bodies is powerful enough to stretch them both, so they wind up shaped a little like two eggs with their ends pointing toward one another. On Earth, the tension has an especially strong effect on the oceans, because water moves so freely, and is the driving force behind tides.

Illustration of Earth as seen from the moon. The gravitational tug-of-war between Earth and the moon raises a small bulge on the moon. The position of this bulge shifts slightly over time.
Credit: NASA's Goddard Space Flight Center

Scientists combined observations from two NASA missions to check out the moon's lopsided shape and how it changes under Earth's sway -- a response not seen from orbit before.

The team drew on studies by NASA's Lunar Reconnaissance Orbiter, which has been investigating the moon since 2009, and by NASA's Gravity Recovery and Interior Laboratory, or GRAIL, mission. Because orbiting spacecraft gathered the data, the scientists were able to take the entire moon into account, not just the side that can be observed from Earth.

"The deformation of the moon due to Earth's pull is very challenging to measure, but learning more about it gives us clues about the interior of the moon," said Erwan Mazarico, a scientist with the Massachusetts Institute of Technology in Cambridge, Mass., who works at NASA's Goddard Space Flight Center in Greenbelt, Md.

The lopsided shape of the moon is one result of its gravitational tug-of-war with Earth. The mutual pulling of the two bodies is powerful enough to stretch them both, so they wind up shaped a little like two eggs with their ends pointing toward one another. On Earth, the tension has an especially strong effect on the oceans, because water moves so freely, and is the driving force behind tides.

Earth's distorting effect on the moon, called the lunar body tide, is more difficult to detect, because the moon is solid except for its small core. Even so, there is enough force to raise a bulge about 20 inches (51 centimeters) high on the near side of the moon and similar one on the far side.

The position of the bulge actually shifts a few inches over time. Although the same side of the moon constantly faces Earth, because of the tilt and shape of the moon's orbit, the side facing Earth appears to wobble. From the moon's viewpoint, Earth doesn't sit motionless but moves around within a small patch of sky. The bulge responds to Earth's movements like a dance partner, following wherever the lead goes.

"If nothing changed on the moon -- if there were no lunar body tide or if its tide were completely static -- then every time scientists measured the surface height at a particular location, they would get the same value," said Mike Barker, a Sigma Space Corporation scientist based at Goddard and co-author of the new study, which is available online in Geophysical Research Letters.

A few studies of these subtle changes were conducted previously from Earth. But not until LRO and GRAIL did satellites provide enough resolution to see the lunar tide from orbit.

To search for the tide's signature, the scientists turned to data taken by LRO's Lunar Orbiter Laser Altimeter, or LOLA, which is mapping the height of features on the moon's surface. The team chose spots that the spacecraft has passed over more than once, each time approaching along a different flight path. More than 350,000 locations were selected, covering areas on the near and far sides of the moon.

The researchers precisely matched measurements taken at the same spot and calculated whether the height had risen or fallen from one satellite pass to the next; a change indicated a shift in the location of the bulge.

A crucial step in the process was to pinpoint exactly how far above the surface LRO was located for each measurement. To reconstruct the spacecraft's orbit with sufficient accuracy, the researchers needed the detailed map of the moon's gravity field provided by the GRAIL mission.

"This study provides a more direct measurement of the lunar body tide and much more comprehensive coverage than has been achieved before," said John Keller, LRO project scientist at Goddard.

The good news for lunar scientists is that the new results are consistent with earlier findings. The estimated size of the tide confirmed the previous measurement of the bulge. The other value of great interest to researchers is the overall stiffness of the moon, known as the Love number h2, and this was also similar to prior results.

Having confirmation of the previous values -- with significantly smaller errors than before -- will make the lunar body tide a more useful piece of information for scientists.

"This research shows the power of bringing together the capabilities of two missions. The extraction of the tide from the LOLA data would have been impossible without the gravity model of the moon provided by the GRAIL mission," said David Smith, the principal investigator for LRO's LOLA instrument and the deputy principal investigator for the GRAIL mission. Smith is affiliated with Goddard and the Massachusetts Institute of Technology.


Story Source:

The above story is based on materials provided by NASA/Goddard Space Flight Center. The original article was written by Elizabeth Zubritsky. Note: Materials may be edited for content and length.


Cite This Page:

NASA/Goddard Space Flight Center. "NASA missions let scientists see moon's dancing tide from orbit." ScienceDaily. ScienceDaily, 29 May 2014. <www.sciencedaily.com/releases/2014/05/140529142540.htm>.
NASA/Goddard Space Flight Center. (2014, May 29). NASA missions let scientists see moon's dancing tide from orbit. ScienceDaily. Retrieved July 29, 2014 from www.sciencedaily.com/releases/2014/05/140529142540.htm
NASA/Goddard Space Flight Center. "NASA missions let scientists see moon's dancing tide from orbit." ScienceDaily. www.sciencedaily.com/releases/2014/05/140529142540.htm (accessed July 29, 2014).

Share This




More Space & Time News

Tuesday, July 29, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Russia Saves Gecko Sex Satellite, Media Has Some Fun With It

Russia Saves Gecko Sex Satellite, Media Has Some Fun With It

Newsy (July 27, 2014) The satellite is back under ground control after a tense few days, but with a gecko sex experiment on board, the media just couldn't help themselves. Video provided by Newsy
Powered by NewsLook.com
NASA EDGE: OCO-2 Launch

NASA EDGE: OCO-2 Launch

NASA (July 25, 2014) NASA EDGE webcasts live from Vandenberg AFB for the launch of the Oribiting Carbon Observatory-2 (OCO) launch. Video provided by NASA
Powered by NewsLook.com
This Week @ NASA, July 25, 2014

This Week @ NASA, July 25, 2014

NASA (July 25, 2014) Apollo 11 celebration, Next Giant Leap anticipation, ISS astronauts appear in the House and more... Video provided by NASA
Powered by NewsLook.com
Space to Ground: Coming and Going

Space to Ground: Coming and Going

NASA (July 25, 2014) One station cargo ship leaves, another arrives, aquatic research and commercial spinoffs. Questions or comments? Use #spacetoground to talk to us. Video provided by NASA
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins