Mars rarely passes directly behind the sun from Earth, and it won’t this year. But, for a period centered on July 27, 2017, it’ll be near the sun on the sky’s dome, crossing the sky with the sun during the day. Astronomers call this location of Mars in our sky a conjunction, and, around every Mars conjunction with the sun, NASA has a moratorium on sending commands to its Mars spacecraft. On July 14, NASA announced that this year’s moratorium will happen from July 22 to August 1. Chad Edwards, manager of the Mars Relay Network Office at NASA’s Jet Propulsion Laboratory, Pasadena, California, said:
Out of caution, we won’t talk to our Mars assets during that period because we expect significant degradation in the communication link, and we don’t want to take a chance that one of our spacecraft would act on a corrupted command.
However, Edwards said:
We will continue to receive telemetry, so we will have information every day about the status of the vehicles.
Loss or corruption of some bits of data coming from Mars is anticipated. The data will be retransmitted later.
NASA said that the upcoming total solar eclipse on August 21 will give people a visible lesson on why signals between Earth and Mars can be corrupted, even when Mars isn’t directly behind the sun.
The sun’s corona, which always extends far from the surface of the sun, becomes visible during total eclipses. It consists of hot, ionized gas, which can interfere with radio waves that pass through it.
NASA said its teams that operate Mars orbiters and rovers have been preparing for weeks in anticipation of the upcoming moratorium on commands. They’re currently determining the most useful sites for the rovers Curiosity and Opportunity to remain productive during the solar-conjunction period. Mars Program Chief Engineer Hoppy Price, of JPL, said:
The vehicles will stay active, carrying out commands sent in advance. Orbiters will be making their science observations and transmitting data. The rovers won’t be driving, but observations and measurements will continue.
NASA said all of its spacecraft on or orbiting Mars have experience from at least one previous Mars conjunction.
This will be the eighth solar conjunction period for the Mars Odyssey orbiter, the seventh for the Opportunity rover, the sixth for the Mars Reconnaissance Orbiter, the third for the Curiosity rover and the second for the MAVEN orbiter.
All of these spacecraft are now veterans of conjunction. We know what to expect.
Bottom line: Mars will be in conjunction with the sun on July 27, 2017. NASA will refrain from sending commands to its spacecraft between July 22 and August 1, so that the spacecraft don’t act on commands corrupted by passing too near the sun.
Deborah Byrd created the EarthSky radio series in 1991 and EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.