Space. Towards a resumption of Uranus exploration?

Victim of a name that turns out to be an inexhaustible source of dubious jokes (if you already find it funny in French, imagine it pronounced in English), is Uranus the most despised of the planets in the solar system? One of the least known, in any case. Although about 40 spacecraft have been sent to Mars and some 30 to Venus, only one has ever approached Uranus: Voyager 2, which briefly passed through it in January 1986 before continuing its journey to the confines of solar system.

Since then, almost nothing. Through telescopes, we detected a dozen additional small satellites, discovered by taking data from Voyager 2 that part of its atmosphere was escaping into space, or was mocked after being shown to contain sulfur d ‘hydrogen and therefore Uranus probably smelled of fart. . But no machine has ever made its way to the seventh planet in the solar system.

And this negligence has lasted long enough, scientists say. In its ten-year report, the American Academy of Sciences, Engineering, and Medicine judges that sending a probe to Uranus should have the highest possible priority for the 2023-2032 decade. “Uranus is one of the most intriguing bodies in the solar system: its low internal energy, its atmospheric dynamics, its complex magnetic field are important mysteries,” the report notes.

Uranus, photographed by the Voyager 2 spacecraft in 1986. Photo Nasa

Four times larger than Earth, Uranus is with Neptune part of the family of ice giants. Located three billion kilometers from the Sun, which takes 84 years to circulate, is a planet composed essentially of water, ammonia and methane in solid form (which is present in small proportions in an atmosphere composed mainly of hydrogen and helium gives it the its bluish tint). Like the other three giant planets, Saturn, Jupiter and Neptune, it also has several rings: discovered in the late 1970s, there are thirteen, dark in color and made up of particles that can sometimes reach several meters.

Uranus also has 27 satellites of different sizes, named after Shakespeare’s characters. The largest, Titania and Oberon, are about 1,500 km in diameter.

A frozen ball of gas and liquid

But several features distinguish it from other planets in the solar system, starting with its axis of rotation, almost aligned with the plane of the ecliptic: Uranus “rolls” almost over its orbit and alternately has its south pole and north pole. to the Sun. In these regions, day and night last half a revolution, or 42 years! Scientists believe that an impact with a celestial body could be the cause of this atypical tilt, to say the least.

Another curiosity: its winds, among the most violent in the solar system after those of Neptune: can reach 850 km / h, and change direction to the equator. Either these bright clouds or these storms, then lost by Voyager 2, but detected several times since then by telescopes, and on which specialists are lost in conjecture.

The most obvious originality of Uranus: its axis of rotation! It almost rolls in its orbit, like a ball.

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Uranus is also the coldest planet in the solar system, with atmospheric temperatures ranging from -226 ° C to -197 ° C. This is even less than in Neptune, which is farther from the Sun, and close to the temperatures that can be found on the surface of Pluto, six billion kilometers from our star.

Amazing, Uranus? Some studies have even shown that it could theoretically rain diamonds there, in the depths of the planet under enormous pressures where methane could be transformed into pure carbon. And that counts without the recent discovery, using data from Voyager, of a giant plasmoid: a huge magnetic bubble that would accelerate evaporation into space from the planet’s atmosphere.

In short, the ice giant could be a great playground for scientists, and even prove to be richer in lessons than telluric planets like Mars. But before you see a spacecraft orbiting Uranus, be patient: if the project is held back by NASA, as is often the case with American National Academy proposals, the spacecraft should not take off. before 2031-2032, the next window of opportunity to limit the trip to “only” thirteen years, and therefore not reach the sight of Uranus before 2044 …

A catalog of missions for the next twenty years

Sending a probe to Uranus is not the only mission classified as a “high priority” by the American Academy of Sciences, Engineering, and Medicine in its 10-year report released Tuesday. Scientists are also proposing to send a probe to Enceladus, one of Saturn’s moons, considered by its geysers to be a possible candidate for the existence of extraterrestrial life forms. As well as many other smaller projects, ranging from sending a rock-picking robot to the moon, to flying over Triton, a moon of Neptune, to various comet sampling missions, or to planet of Ceres.

The proposals of the American Academy of Sciences are often followed by NASA, which extracts the major missions of the next decade. The Mars Sample Return mission, which envisions the return to Earth of Martian samples currently collected by Perseverance, was mentioned in the previous 2011 report.

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