While robotic rovers may explore the surface of Mars on behalf of humans who can't safely land there yet, they aren't alone.
A fleet of orbiters circling the planet act as dual-purpose workhorses, relaying back data and images from the surface missions to Earth while studying various aspects of the planet.
Their mapping capabilities have allowed NASA mission teams to select intriguing landing sites, and their cameras and instruments can keep watch on surface missions and even warn of global dust storms.
When NASA's Perseverance rover lands on Mars on February 18, it will be the most sophisticated robotic explorer yet to venture across the Martian surface. The rover will search for signs of ancient life at the site of Jezero Crater, where a river delta and lake existed 3.9 billion years ago.
The rover will regularly talk to orbiters that swing around Mars, primarily NASA's Mars Reconnaissance Orbiter, or MRO. This orbiter, which arrived at Mars in 2006, will act as the main communications relay to send back data and images gathered by the rover.
Orbiters like MRO and MAVEN, or Mars Atmosphere and Volatile EvolutioN, will help us know when the Perseverance rover lands next week and receive any of the first photos and sounds -- since this newest rover has two microphones -- it sends our way.
These are just two of the orbiters currently exploring Mars, which also include NASA's 2001 Mars Odyssey orbiter and the European Space Agency's Mars Express orbiter and ExoMars Trace Gas Orbiter, a collaboration between ESA and Roscosmos, Russia's space agency. Earlier this week, they were joined by the United Arab Emirates' and China's orbiter, with the latter planning to land a rover on the Martian surface later this year.
These orbiters, along with all of the other missions currently exploring our solar system, send back information through NASA's . This "invisible network" of communications relayed through space reaches three ground-based giant radio antennas equidistant from one another.
They are located near Madrid in Spain, Canberra in Australia and Goldstone, near Barstow, California. The placement of each giant dish allows for constant contact with space missions as Earth turns.
The Deep Space Network allows for communications with spacecraft as well as tracking their location -- all of which will be imperative during Perseverance's landing on Mars and its mission in the following years.
A GLOBAL PERSPECTIVE
The orbiters aren't just there to help relay information from the InSight lander, the Curiosity rover and the upcoming Perseverance rover. These spacecraft carry suites of instruments and cameras that have made remarkable discoveries about Mars and laid the foundation for future exploration.
The Mars Reconnaissance Orbiter carries the highest-resolution camera around Mars, called the High Resolution Imaging Science Experiment, or HiRISE. It has provided unprecedented views of surface features on Mars, said Leslie Tamppari, deputy project scientist for MRO.
While it has captured images showing vast expanses of the Martian terrain, this camera also can focus in on features as small as a kitchen table. The mission has also mapped almost the entire planet.
Altogether, it has six instruments that have helped to understand more about the history of water on Mars as well as seasonal features on Mars, like dust storms or landslides called Recurring Slope Lineae.
The mission has discovered ice beneath the surface of Mars, even in places like the midlatitudes where it appears there were ancient glaciers, Tamppari said.
The orbiter has been circling Mars since 2006, so the team has been able to track changes on the Martian surface over time -- an invaluable tool when trying to understand a world so different from our own.
"The more we look, the more we discover," Tamppari said.
One of the key questions around Mars is what happened to the planet. Scientists believe that Mars was a warmer, wetter planet with a thick atmosphere billions of years ago -- much like early Earth -- which means Mars was likely habitable. Then, the atmosphere and water were stripped away.
Data collected by MRO and MAVEN is helping scientists understand how Mars lost so much water over 4 billion years. While MRO has been able to study an area ranging from the Martian subsurface to 49 miles above the surface, MAVEN has focused on the upper atmosphere.
The MAVEN orbiter arrived at Mars in 2014, the first mission devoted to studying the upper atmosphere of Mars and understanding how it interacts both with the lower atmosphere as well as the sun and the solar wind (which are actually charged particles that stream out from the sun), said Bruce Jakosky, principal investigator for the MAVEN mission.
One of the main goals for the MAVEN mission has been to understand the processes that stripped away the Martian atmosphere over time.
"The bulk of the Martian atmosphere has been lost to space through time," Jakosky said. "It's the major component in explaining Martian climate change, from a warmer, wetter environment to the colder, drier environment we see today. That stands out as the most important discovery for MAVEN so far."
Both spacecraft continue to be healthy and will continue forward with their science goals as they orbit Mars.
ALL EYES ON THE LANDING
Images and data collected by the Mars Reconnaissance Orbiter helped with the selection of Perseverance's landing site of Jezero Crater. So it's only fitting that MRO will be Perseverance's main point of contact.
Ahead of the landing, MRO is keeping an eye on the Martian atmospheric conditions. On landing day, MRO will be standing by to pick up all of the crucial information Perseverance transmits through every stage of entry into the atmosphere, the descent through it and landing on the surface.
That information will be sent back to Earth as MRO receives it.
There is, of course, the natural delay caused by distance -- it's an 11-minute delay one way between Mars and Earth.
The rovers need the orbiters to help them talk to Earth because while they have small antennas that could reach Earth, these can't be used to send back all of the data in a timely manner.
Some of the instruments on MRO can cause interference, so these will be shut off during the communication relay. Fortunately, MRO's HiRISE camera is not one of those that causes interference. Team scientists will attempt to capture an image of the Perseverance rover as it descends through the atmosphere with its parachutes open, as they did during the landing for Curiosity.
Once Perseverance lands, MRO can use its camera to capture images of the landing site -- as soon as the day after landing.
The MAVEN orbiter will also be used to collect data from Perseverance as it enters the atmosphere and lands -- and data from the orbiter could also be used to figure out what happened should anything go wrong during landing, Jakosky said.
After the landing, MAVEN will also support the Curiosity rover.
Many of the members of the MAVEN team are also on the Hope Probe team, including Jakosky, and he anticipates a strong collaboration between the two missions as they investigate the atmosphere of Mars.
"This promises to be an exciting time at Mars," Jakosky said.
