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  • Do you remember hearing about that weird, strange-shaped

  • object that passed through our inner solar system late last

  • year? It was the first object we've confirmed to have come

  • from outside our solar system, and was given the name

  • 'Oumuamua, Hawaiian forscout or messenger from our distant

  • past.” Now, scientists have analyzed data from many

  • observatories, including NASA's Hubble Space Telescope, and

  • found that this interstellar object has gained an unexpected

  • boost of speed. After 'Oumuamua was discovered with Hawaii's

  • Pan-STARRS 1 telescope as it surveyed the skies for

  • near-Earth asteroids in October 2017, observatories all around

  • and above the world focused on the approximately half-mile long

  • object to learn as much as possible about this cosmic

  • visitor before it flew too far away to see. The Hubble Space

  • Telescope was used to collect observations to determine the

  • object's trajectory over two months in late 2017 and early

  • 2018. The observations were combined with data from multiple

  • ground-based observatories, which showed 'Oumuamua to have a

  • small, continuous non-gravitational

  • acceleration.” Something besides just the gravity from

  • the Sun and planets was affecting the trajectory of

  • 'Oumuamua. A probable source of this acceleration is jets of gas

  • coming off the object. This behavior is similar to objects

  • we have already identified as cometswhen they get close to

  • the Sun, ices in the comet sublimate into gas, and

  • streamers of gas can push the object along. Usually when

  • comets do this the outgassing can be seen because it ejects

  • large amounts of dust, which form a cloud around the object,

  • called a coma, and a tail. But with 'Oumuamua, no type of coma

  • or tail was seen. Maybe 'Oumuamua doesn't have much dust

  • left after its interstellar journeyan amount no more than

  • a couple coffee cans of material, making the dust too

  • sparse for us to see. Or, maybe the dust was much larger than

  • normal, making it hard for us to detect. I know that sounds

  • counterintuitive, but it's easiest to detect dust when the

  • particles are similar in size to the wavelength of light we're

  • using. Observatories were looking at 'Oumuamua in visible

  • light, where we have the most sensitive detectors, but larger

  • particles of dust would be easier to detect with microwave

  • or radio wavelengths. This is definitely an unusual object,

  • and unfortunately no more new observations of 'Oumuamua are

  • possible because it's already too dim and far away for even

  • Hubble to see. But when there's one weird object there are

  • probably more. Sky survey programs will keep an eye out

  • for other interstellar visitors, and the Hubble Space Telescope

  • will be ready to contribute observations to better

  • understand any more orphaned vagabonds traveling between the

  • the stars.

  • www.nasa.gov/hubble @NASAHubble

Do you remember hearing about that weird, strange-shaped

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オウムアムアは恒星間小惑星か彗星か? (Is Oumuamua an Interstellar Asteroid or Comet?)

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    Richard VT に公開 2021 年 01 月 14 日
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