A new global map of Mars offers a fresh perspective on the planet.
The map, released earlier this month, was pieced together from 3,000 pictures taken by the United Arab Emirates’ Hope spacecraft, and it shows the red planet in its true light.
“These are all natural colors on Mars,” said Dimitra Atri, a research scientist at the Center for Space Science at N.Y.U. Abu Dhabi.
The main scientific objective of Hope, which entered orbit around Mars a little more than two years ago, is to study how dust storms and other weather conditions near the surface affect the speed at which Martian air leaks into outer space.
But the orbiter also carries a camera.
When Dr. Atri saw the first image sent back by Hope, “I was just blown away by the quality of the image showing the full disk,” he said. “I had never seen Mars like this.”
Maps of Mars are nothing new. In the 1890s, the American businessman Percival Lowell used his wealth to build the Lowell Observatory in Flagstaff, Ariz., and as he gazed at Mars through a 24-inch telescope, he sketched what he thought were artificial canals built by a Martian civilization. (He observed spokelike structures on Venus; it was later demonstrated that he may have inadvertently turned his telescope into a mirror and was viewing the back of his own eyeball.)
In the space age, numerous spacecraft have flown past Mars or entered orbit around it.
But previous orbiters, like NASA’s Mars Global Surveyor and Mars Reconnaissance Orbiter, have generally swooped much closer to the Martian surface, usually in orbits devised to repeatedly pass above a given location at the same time of day. Those images have provided increasingly sharp details of the surface, including sand dunes, gullies and boulders that had rolled down hills.
“Those are amazing, spectacular images,” Dr. Atri said. “But you don’t see the whole planet at once.” Lighting conditions that varied from place to place made it difficult to put together a single, global view.
Lighting conditions are not a problem for other types of maps. The Global Surveyor carried an altimeter instrument that bounced a laser beam off the surface. By measuring the time the pulse of light took to travel to the surface and back, the instrument could measure the height of every nook and cranny on the surface. Scientists used the data to make a detailed topographic map.
For views in visible light, the Hubble Space Telescope, in orbit around Earth, can see one entire side of Mars. Scientists pieced together many such images into a global map similar to the new map from the Hope spacecraft.
But Mars, at its closest, is nearly 34 million miles from Earth, so the Hubble images lack sharpness. Hope travels around Mars in an elliptical orbit ranging from 12,400 miles to 27,000 miles above the Martian surface. That is considerably higher up than the Mars Reconnaissance Orbiter, but much closer than Hubble.
“We thought, OK, we should have an atlas, because we may be able to photograph Mars over a period of several years,” Dr. Atri said. “So we should first have an atlas where we not only map the whole planet, but we show how it changes throughout the Martian year.”
Dr. Atri was able to find images with similar lighting conditions to stitch together, omitting ones in which clouds obscured the surface. The process took months. “It is extremely hard to remove all the boundaries and stuff,” he said.
Dr. Atri said that he and his colleagues were currently writing a scientific paper to describe the algorithm they devised. The same method could be applied to other spacecraft visiting other worlds, including the European Space Agency’s Jupiter Icy Moons Explorer, or Juice, which launched on Friday.
“These icy moons look so pretty,” Dr. Atri said. “So we should be able to apply the same technique.”
