[ti:Scientists Identify Polar Cyclone on Uranus]
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[00:00.04]The seventh planet from the sun, Uranus,
[00:04.56]is a world surrounded by mystery.
[00:07.68]Seen up close just once nearly forty years ago
[00:11.92]by a passing NASA spacecraft,
[00:14.80]the planet still guards many secrets.
[00:17.76]But new observations are providing
[00:21.16]a fuller understanding of its atmosphere.
[00:24.92]These observations, made from a telescope
[00:28.76]located in New Mexico,
[00:31.04]include the detection of a polar cyclone
[00:34.76]whose center measures a quarter of Earth's diameter.
[00:39.16]Uranus is a kind of planet known as an ice giant,
[00:44.36]like its planetary neighbor Neptune.
[00:47.56]Scientists were able to look more deeply
[00:51.08]into the atmosphere of Uranus than ever before.
[00:55.68]And the findings painted a picture of a planet
[00:59.64]that is more unusual than previously known.
[01:03.60]Alex Akins of NASA's Jet Propulsion Laboratory in California
[01:09.76]was the lead writer of the research
[01:12.72]published in Geophysical Research Letters.
[01:16.60]While Neptune and Uranus are similar,
[01:20.04]Akins said Uranus "has some pretty unique features."
[01:24.96]"It spins on its side. And even then,
[01:28.56]its magnetic field is still misaligned with its rotational axis.
[01:34.44]The atmospheric circulation and internal heat release
[01:38.76]appear weaker than Neptune, but there are still a range of ...
[01:43.72]features and storms that have been observed," Akins added.
[01:49.16]Uranus is the third-largest planet in our solar system.
[01:54.36]It has a diameter of about 50,700 km
[02:00.40]and is big enough to fit 63 Earths inside it.
[02:05.32]Uranus orbits the sun at a distance of about 2.9 billion km,
[02:12.04]almost 20 times further than Earth does.
[02:16.24]One orbit lasts 84 years.
[02:20.24]Its unusual tilt makes Uranus
[02:23.24]appear to orbit the sun like a rolling ball.
[02:27.56]The researchers used the Very Large Array telescope in New Mexico
[02:33.56]to see below the clouds at the top of the atmosphere.
[02:37.96]They found moving air at the north pole
[02:41.24]that was warmer and drier,
[02:43.80]evidence of a strong cyclone.
[02:46.76]Researchers were able to estimate the size of the storm's center
[02:51.68]but not the entire cyclone's diameter.
[02:55.08]It is possible that the cyclone was wider than Earth.
[02:59.52]The research suggested that polar cyclones
[03:03.00]exist on many bodies in our solar system
[03:06.72]- all the planets except Mercury and Saturn's moon Titan.
[03:12.28]Most of the mass of Uranus is a fluid of icy materials
[03:17.48]- water, methane and ammonia.
[03:20.72]Uranus is surrounded by two sets of rings
[03:24.96]and orbited by 27 small moons.
[03:28.48]Its atmosphere is the coldest of any of the eight planets,
[03:33.72]including outermost Neptune.
[03:36.32]Uranus' only close meeting with a spacecraft
[03:40.60]came when Voyager 2 flew by in 1986.
[03:45.52]"There are a lot of unknowns," Akins said about Uranus.
[03:50.32]"How did it get tilted on its side?
[03:53.76]Is its interior really 'icier' than the gas giants (Jupiter and Saturn)? …
[03:59.72]Why is the pole so much drier than the equator?
[04:03.68]Are its satellites (moons) ocean worlds?"
[04:07.00]I'm John Russell. 更多听力请访问21VOA.COM