Lost Reflector Found on the Moon

Apr 27, 2010
Lost Reflector Found on the Moon
(Rover Parking Spot): The Lunokhod 1 rover in its final parking spot on the moon. Credit: NASA/GSFC/Arizona State U.

Physicists have pinpointed the location of a long lost light reflector left on the Moon by the Soviet Union nearly 40 years ago. The reflector could actually help today's scientists measure physical properties of the Moon and phenomena such as tidal distortion.

A team of physicists led by a professor at UC San Diego has pinpointed the location of a long lost light left on the by the Soviet Union nearly 40 years ago that many scientists had unsuccessfully searched for and never expected would be found.

The French-built laser reflector was sent aboard the unmanned Luna 17 mission, which landed on the Moon November 17, 1970, releasing a robotic rover that roamed the lunar surface and carried the missing laser reflector. The Soviet lander and its rover, called Lunokhod 1, were last heard from on September 14, 1971.

“No one had seen the reflector since 1971,” said Tom Murphy, an associate professor of physics at UCSD. He heads a team of scientists engaged in a long-term effort to look for deviations of Einstein’s theory of general relativity by measuring the shape of the to within an accuracy of one millimeter, or about the thickness of a paperclip. This is accomplished by timing the reflections of pulses of laser light from reflectors left on the Moon by Apollo astronauts and turning the timing measurement into a distance.

“We routinely use the three hardy reflectors placed on the Moon by the , 14 and 15 missions,” said Murphy, “and occasionally the Soviet-landed Lunokhod 2 reflector -- though it does not work well enough to use when illuminated by sunlight. But we yearned to find Lunokhod 1.”

Three reflectors are required to lock down the orientation of the Moon. A fourth adds information about tidal distortion of the Moon, and a fifth enhances that information.

“Lunokhod 1, by virtue of its location, would provide the best leverage for understanding the liquid lunar core, and for producing an accurate estimate of the position of the center of the Moon -- which is of paramount importance in mapping out the orbit and putting Einstein’s gravity to a test,” said Murphy.

Murphy said his team had occasionally looked for the Lunokhod 1 reflector over the last two years, but faced tall odds against finding it until recently. The breakthrough came last month when the high-resolution camera on NASA’s Lunar Reconnaissance Orbiter, or LRO, obtained images of the landing site. The camera team, led by Mark Robinson at Arizona State University, identified the rover as a sunlit speck on the image -- miles from where Murphy and his team had been searching. But until now the existence of the reflector or its precise location was unknown.

Lost Reflector Found on the Moon
(Soviet Rover) The Soviet Lunokhod rovers were about 2.3 meters long and 1.5 meters tall.

“It turns out we were searching around a position miles from the rover,” said Murphy. “We could only search one football-field-sized region at a time. The recent images from LRO, together with laser altimetry of the surface, provided coordinates within 100 meters, and then we were in business and only had to wait for time on the telescope in good observing conditions.”

On April 22, his team sent pulses of laser light from the 3.5 meter telescope at the Apache Point Observatory in New Mexico, zeroing in on the target coordinates provided by the LRO images. Murphy, together with Russet McMillan of the Apache Point Observatory in Sunspot, NM, and UCSD physics graduate student Eric Michelsen found the long lost Lunokhod 1 reflector and pinpointed its distance from Earth to within one centimeter. They then made a second observation less than 30 minutes later that allowed the team to triangulate the reflector’s latitude and longitude on the Moon, in other words its exact spot on the Moon, to within 10 meters -- ”not bad for a half-hour’s work,” said Murphy. In the coming months, he estimates it will be possible to establish the reflector’s coordinates to better than one-centimeter precision.

The return signal from the reflector was measured by Murphy’s team as a collection of individual particles, or photons, of laser light.

“We quickly verified the signal to be real and found it to be surprisingly bright: at least five times brighter than the other Soviet reflector, on the Lunokhod 2 rover, to which we routinely send laser pulses,” Murphy said. “The best signal we’ve seen from Lunokhod 2 in several years of effort is 750 return photons, but we got about 2,000 photons from Lunokhod 1 on our first try. It’s got a lot to say after almost 40 years of silence.”

A retroreflector is a set of three mirrors, each at a perpendicular angle to the others, that will reflect light directly back in the direction from which it came. Credit: Solar Physics/Montana State University

The discovery of the Soviet reflector came as a surprise, because scientists had actively searched for it for nearly four decades without success. Many scientists had speculated that the Lunokhod 1 rover might have fallen into a crater or parked badly, with its reflector not facing the Earth, which would have prevented it from being located by laser pulses.

“Not only now do we know that Lunokhod 1 is there, we also know that it is parked perfectly so that its reflector faces Earth,” said Murphy. “In fact, the signal is so surprisingly strong that the rover could not be in anything but a level parking spot with its last commanded roll on the lunar surface deliberately oriented toward the Earth.”

Murphy and his colleagues found in a study they published this month that lunar dust may be obscuring the reflectors on the Moon. His team found that the they bounce off reflectors on the Moon is fainter than expected and dims even more whenever the Moon is full.

“Near full Moon, the strength of the returning light decreases by a factor of ten,” he adds. “We need to understand what is causing this if we are contemplating putting additional scientific equipment on the Moon. Finding the Lunokhod 1 reflector will add important clues to this study.”

Studying the Moon is important to astrobiologists because our nearest celestial neighbor can have a profound influence on the Earth and our biosphere. For instance, many scientists believe that the effects the tides of Earth's oceans.

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thermodynamics
5 / 5 (10) Apr 27, 2010
What???? They say: "For instance, many scientists believe that the Moon effects the tides of Earth's oceans." Only "many scientists?" Does anyone believe that there are other "scientists" who do not believe that the Moon effects the ocean tides? What kind of reporting is this when they couch something as well known as the effect of the moon on tides as some issue that only "many scientists" agree on? This is an incredible statement.
Skeptic_Heretic
5 / 5 (6) Apr 27, 2010
Does anyone believe that there are other "scientists" who do not believe that the Moon effects the ocean tides?

They're called "Christian Scientists", and no, they're not real scientists.

Obviously the author got the two confused.
LuckyBrandon
1 / 5 (1) Apr 27, 2010
I'm wondering if its possible that the suns reflection on the moon is "stealing" light from the reflectors...
fuzz54
5 / 5 (1) Apr 27, 2010
I'm wondering if its possible that the suns reflection on the moon is "stealing" light from the reflectors...
In most cases the sun is hitting the moon and the moon emits light wavelengths according to what it is composed of. That is why grass is green and not some other color. I'm guessing the lasers they use are not in a strong part of the emittance spectrum for the moon light. But hey, that's just me taking an educated guess.
jgelt
1 / 5 (1) Apr 27, 2010
Perhaps full exposure to the sun produces some lunar atmosphere?
phlipper
3.3 / 5 (4) Apr 27, 2010
With very few exceptions, science writers are not able to grasp even the simplest concepts of science. That's why they are writers and not scientists. Sometimes, you just have to laugh.
hush1
not rated yet Apr 28, 2010
In most cases the sun is hitting the moon and the moon emits light wavelengths according to what it is composed of. That is why grass is green and not some other color.[q/]

I conjecture grass is not green on any planet that does not have an atmospheric(chemical)composition such as the earth.

I conjecture the (visible)wavelengths that are able to reach the grass, which are not absorbed from the atmosphere beforehand (or those wavelengths re-emitted from the atmosphere), are the wavelengths that are absorbed by the grass.
The wavelengths of 'colors' we call green, are the (re-)emitted wave light spectrum of the grass's composition.


Yes, of course. An object's color is simply a reflection of, and/or re-emission of wavelengths
defined by compositional makeup. Makes sense.

Don't we define literally everything by the way it distributes energy introduced to it?

Or does Heisenberg's Uncertainty Principle wreak havoc with this simple question?
gwrede
3 / 5 (2) Apr 28, 2010
For instance, many scientists believe that the Moon effects the tides of Earth's oceans.


Either the "writer" is an idiot, a wise gyu, or he is a closet Creationist. Any of these is reason to fire him from PhysOrg. IMNSHO !!

If this kind of scientific quality is accepted by PhysOrg, then literate readers will seek other sources of science news.
KBK
3 / 5 (2) Apr 28, 2010
What???? They say: "For instance, many scientists believe that the Moon effects the tides of Earth's oceans." Only "many scientists?" Does anyone believe that there are other "scientists" who do not believe that the Moon effects the ocean tides? What kind of reporting is this when they couch something as well known as the effect of the moon on tides as some issue that only "many scientists" agree on? This is an incredible statement.


Obviously the reporter was educated in Texas. Or was that Utah?
Msean1941
5 / 5 (1) Apr 29, 2010
Not only doesn't he know science, he also doesn't know English. It's "affects", not "effects". I also can't stand seeing the word "believe" in a science article. "Hypothesize", maybe, but not "believe".
Scott221
5 / 5 (1) May 01, 2010
What???? They say: "For instance, many scientists believe that the Moon effects the tides of Earth's oceans." Only "many scientists?" Does anyone believe that there are other "scientists" who do not believe that the Moon effects the ocean tides? What kind of reporting is this when they couch something as well known as the effect of the moon on tides as some issue that only "many scientists" agree on? This is an incredible statement.


I was shocked too & pretty much had the same reaction. Couldn't help but notice: "Provided by University of California - San Diego". It's probably a reprint that should have been edited. Someone messed up.