While spacecraft duck and cover, they grab historical data about the comet, its effect on Mars
Just as NASA's Mars orbiters took shelter from a debris-spewing comet behind the Red Planet on Sunday, they also took the opportunity to study the flyby's effect on Mars.
Scientists also are hoping to use the orbiters' observations to gain new clues about the origin of our solar system.
"We're glad the spacecraft came through," said Bruce Jakosky, NASA's principal investigator for its Maven spacecraft. "We're excited to complete our observations of how the comet effects Mars, and we're eager to get to our primary science phase."
NASA has been preparing for the flyby of the comet, known as Comet C/2013 A1 Siding Spring, for several months. While scientists worked to position its three orbiters -- the Mars Odyssey, the Mars Reconnaissance Orbiter and the Mars Atmosphere and Volatile Evolution orbiter -- on the opposite side of the planet during the flyby, they also wanted to take advantage of their front-row seat to the event.
"The spacecraft performed flawlessly throughout the comet flyby," said Mars Reconnaissance Orbiter Project Manager Dan Johnston of NASA's Jet Propulsion Laboratory. "It maneuvered for the planned observations of the comet and emerged unscathed."
Comet Siding Spring hurtled past Mars on Sunday at about 125,000 mph, coming within about 87,000 miles of the planet. That is equivalent to about one-third of the distance between Earth and its moon.
NASA reported Sunday night that the closest approach of the comet's nucleus came at about 2:27 p.m. ET. Dust and debris from the comet was reaching Mars at its peak about 100 minutes later.
While the nucleus of the comet was too far away from Mars to affect the orbiters, the comet was shedding material as it passed by. That debris was expected to hurtle toward the planet at 35 miles per second.
NASA noted that at that velocity, even a particle only one-50th of an inch across could cause enough damage that it would be disastrous for the Mars orbiters.
The Martian atmosphere, though thinner than Earth's, should protect the Mars rovers Curiosity and Opportunity from being damaged by any particles flying off the comet.
Without the Martian atmosphere to protect them, the orbiters weren't as safe. That's why NASA maneuvered them to the opposite side of the planet.
The space agency reported that Mars Odyssey was out of communications with Earth, as planned, while conducting observations of the comet with its Thermal Emission Imaging System. The images it captured are expected to be downlinked to NASA and processed this week.
The spacecraft's neutron spectrometer and high-energy neutron detector also are being used to assess the effects the comet's dust and gas are having on Mars' atmosphere.
NASA's Maven spacecraft, which began orbiting the planet on Sept. 21, maintained low-data-rate communications during the comet's flyby, according to the space agency. Maven captured information about the composition of the gases and dust the comet was releasing as it passed by, while also investigating the interaction between the material and the planet's atmosphere.
A downlink of data from the Maven orbiter has already begun.
NASA's Mars Reconnaissance Orbiter also maintained communications with Earth during the Siding Spring's flyby. Its own downlink, which may take days because of the amount of data to send, also has begun.
This orbiter used three instruments to observe the comet for several days as it approached Mars and will continue to take measurements for the next few days as it continues on its path.
Scientists have described the comet's close approach to Mars as a "once-in-a-lifetime opportunity" to study a comet and its affect on the planet's atmosphere, as well as to gain clues about the beginnings of our solar system.
"This is a cosmic science gift that could potentially keep on giving, and the agency's diverse science missions will be in full receive mode," said John Grunsfeld, astronaut and associate administrator for NASA's Science Mission Directorate, in a statement made earlier this month. "This particular comet has never before entered the inner solar system, so it will provide a fresh source of clues to our solar system's earliest days."
The Siding Spring comet -- which came from the Oort Cloud, a spherical region of space surrounding our sun -- is made up of a giant swarm of icy objects believed to be material left over from the formation of the solar system.
It will be the first comet from that region scientists have been able to study up close, giving them a chance to learn more about the materials, including water and carbon compounds, that existed during the formation of the solar system 4.6 billion years ago, NASA noted.