China, the United Arab Emirates, and the United States are going to Mars this summer, The New York Times reported. They include orbiters, landing pods, rovers, and an experimental helicopter to observe and report on the Red Planet from orbit and on land. The orbit and atmosphere of Mars compare oddly to Earth’s.
According to The New York Times, three nations have recently launched unmanned spacecraft bound for Mars. The Hope Orbiter “was the first spacecraft to launch for Mars this summer, and the first Mars mission for the United Arab Emirates,” the article said. It launched on July 19 and will observe Mars from space, studying its upper and lower atmospheres.
On July 23, The Times said, China sent Tianwen-1, “an orbiter, lander, and rover” to Mars, making it “the only mission this year to attempt a three-pronged exploration.” The landing pod will detach from the orbiter and parachute to the planet’s surface, opening to allow a solar-powered land rover to disembark.
Finally, NASA launched two spacecraft from the United States. “The NASA mission includes Perseverance, a 2,200-pound rover; and Ingenuity, an experimental Mars helicopter,” the article said. “The Ingenuity helicopter weighs about four pounds and will be the first to attempt powered flight on another planet.”
None of these missions would be possible if we didn’t have some idea of how to get to Mars and get there safely, which is possible due to a working knowledge of its orbit and atmosphere.
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Some of the planetary attributes of Mars are strangely similar to those of Earth.
“The length of one day-night cycle on Mars, known as a sol, is 24 hours, 39 minutes, and 35 seconds,” said Dr. Sabine Stanley, a Bloomberg Distinguished Professor in the Morton K. Blaustein Department of Earth and Planetary Sciences at Johns Hopkins University. “The fact that this is quite close to the length of a day on Earth is a great coincidence, but it does mean that we wouldn’t have to adjust our internal clocks too much if we were to visit Mars.”
Dr. Stanley said some scientists and engineers who work on Mars missions already sync their schedules to Mars time since they can only communicate with spacecraft on Mars when the spacecraft are facing Earth.
“Mars also has seasons, because the planet’s rotation axis is tilted relative to its orbital axis,” she said. “The tilt is currently about 25°, quite similar to Earth’s tilt of 23.5°.”
However, this is where the similarities end. Dr. Sabine said that due to Mars’s wider orbit around the sun, its year is nearly twice as long as Earth’s, so its seasons last twice as long too. This means summer and winter are each six months on Mars.
All of the Mars-bound spacecraft will at least encounter the Red Planet’s atmosphere, while several will study it closely as well. Unlike Mars’s sol cycle and its tilt, its atmosphere differs greatly from Earth’s—in fact, it barely has one.
“Whereas Venus has a very thick atmosphere, with a surface pressure of about 92 bars (that’s 92 times Earth’s surface pressure), Mars has a very thin atmosphere,” Dr. Stanley said. “The surface pressure on Earth is 200 times that on Mars, which has a surface pressure similar to the lower mesosphere of Earth—too thin to support balloons, but too much friction for satellites.
“The atmosphere Mars does have is 95% carbon dioxide—very similar in composition to Venus. There’s just not much there.”
According to Dr. Stanley, water in the human body boils away at about 6% of Earth’s atmosphere, but pressure on Mars is only about one-tenth of that small amount.
“This very low surface pressure also means that it would be very hard to feel the impact of winds on Mars,” she said. “Even though Mars can have moderately fast winds and storms, with wind speeds around 38 miles per hour, those winds probably wouldn’t knock a person over or break apart antennas on mechanical equipment.”
That’s good news for an increasingly crowded planet.
Dr. Sabine Stanley contributed to this article. Dr. Stanley is a Bloomberg Distinguished Professor in the Morton K. Blaustein Department of Earth and Planetary Sciences at Johns Hopkins University. She received a HBSc degree in Physics and Astronomy from the University of Toronto and then completed MA and PhD degrees in Geophysics from Harvard University.