Hubble sees `Oumuamua getting a boost. New results indicate interstellar nomad is a comet
`Oumuamua — the first interstellar object discovered within our Solar System — has been the subject of intense scrutiny since its discovery in October 2017 [1]. Now, by combining data from the NASA/ESA Hubble Space Telescope, the Canada-France-Hawaii Telescope, ESO’s Very Large Telescope and the Gemini South Telescope, an international team of astronomers has found that the object is moving faster than predicted. The measured gain in speed is tiny and `Oumuamua is still slowing down because of the pull of the Sun — just not as fast as predicted by celestial mechanics.
The team, led by Marco Micheli (European Space Agency) explored several scenarios to explain the faster-than-predicted speed of this peculiar interstellar visitor. The most likely explanation is that `Oumuamua is venting material from its surface due to solar heating — a behaviour known as outgassing [2]. The thrust from this ejected material is thought to provide the small but steady push that is sending `Oumuamua hurtling out of the Solar System faster than expected — as of 1 June, it is travelling with about 114 000 kilometres per hour.
Such outgassing is a typical behaviour for comets and contradicts the previous classification of `Oumuamua as an interstellar asteroid. “We think this is a tiny, weird comet,” comments Marco Micheli. “We can see in the data that its boost is getting smaller the farther away it travels from the Sun, which is typical for comets.”
Usually, when comets are warmed by the Sun they eject dust and gas, which form a cloud of material — called a coma — around them, as well as the characteristic tail. However, the research team could not detect any visual evidence of outgassing.
“We did not see any dust, coma, or tail, which is unusual,” explains co-author Karen Meech (University of Hawaii, USA) who led the discovery team’s characterisation of `Oumuamua in 2017. “We think that ‘Oumuamua may vent unusually large, coarse dust grains.”
The team speculated that perhaps the small dust grains adorning the surface of most comets eroded during `Oumuamua’s journey through interstellar space, with only larger dust grains remaining. A cloud of these larger particles would not be bright enough to be detected by Hubble.
Not only is `Oumuamua’s hypothesised outgassing an unsolved mystery, but also its interstellar origin. The team originally performed the new observations on `Oumuamua to exactly determine its path which would have probably allowed it to trace the object back to its parent star system. The new results means it will be more challenging to obtain this information.
“The true nature of this enigmatic interstellar nomad may remain a mystery,” concludes team member Olivier Hainaut (European Southern Observatory, Germany). “`Oumuamua’s recently-detected gain in speed makes it more difficult to be able to trace the path it took from its extrasolar home star.”
Notes
[1]`Oumuamua, pronounced “oh-MOO-ah-MOO-ah”, was first discovered using the Pan-STARRS telescope at the Haleakala Observatory, Hawaii. Its name means “a messenger from afar, arriving first” in Hawaiian, and reflects its nature as the first known object of interstellar origin to have entered the Solar System.
[2] The team tested several hypotheses to explain the unexpected change in speed. They analysed whether solar radiation pressure, the Yarkovsky effect, or friction-like effects could explain the observations. It was also checked whether the gain in speed could have been caused by an impulse event (such as a collision), by `Oumuamua being a binary object or by `Oumuamua being a magnetised object. Also, the unlikely theory that `Oumuamua is an interstellar spaceship was rejected: the smooth and continuous change in speed is not typical for thrusters and the object is tumbling on all three axes, speaking against it being an artificial object.
Artist’s impression of the interstellar asteroid `Oumuamua
This artist’s impression shows the first interstellar object discovered in the Solar System, `Oumuamua. Observations made with the NASA/ESA Hubble Space Telescope and others show that the object is moving faster than predicted while leaving the Solar System.
Researchers assume that venting material from its surface due to solar heating is responsible for this behaviour. This outgassing can be seen in this artist’s impression as a subtle cloud being ejected from the side of the object facing the Sun.
As outgassing is a behaviour typical for comets, the team thinks that `Oumuamua’s previous classification as an interstellar asteroid has to be corrected.
Credit:
ESA/Hubble, NASA, ESO, M. Kornmesser
Predicted position of `Oumuamua versus observed position
This diagram shows the orbit of the interstellar object ‘Oumuamua as
it passes through the Solar System. It shows the predicted path of
‘Oumuamua and the new course, taking the new measured velocity of the
object into account.
‘Oumuamua passed the distance of Jupiter’s orbit in early May 2018 and will pass Saturn’s orbit January 2019. It will reach a distance corresponding to Uranus’ orbit in August 2020 and of Neptune in late June 2024. In late 2025 ‘Oumuamua will reach the outer edge of the Kuiper Belt, and then the heliopause — the edge of the Solar System — in November 2038.
Credit:
‘Oumuamua passed the distance of Jupiter’s orbit in early May 2018 and will pass Saturn’s orbit January 2019. It will reach a distance corresponding to Uranus’ orbit in August 2020 and of Neptune in late June 2024. In late 2025 ‘Oumuamua will reach the outer edge of the Kuiper Belt, and then the heliopause — the edge of the Solar System — in November 2038.
Credit:
ESA
VIDEOS .
VIDEOS .
Hubblecast 111: Hubble sees `Oumuamua getting a boost
Astronomers have found that ‘Oumuamua, the first interstellar object discovered in the Solar System, is moving away from the Sun faster than expected. Using data from the NASA/ESA Hubble Space Telescope, in cooperation with ground-based telescopes, a team of researchers concluded that ‘Oumuamua is most likely outgassing — suggesting that this enigmatic interstellar nomad is a peculiar comet rather than an asteroid.
Credit:
Directed by: Mathias Jäger
Visual design and editing: Martin Kornmesser
Written by: Calum Turner, Mathias Jäger
Narration: Sara Mendes da Costa
Images: ESA/Hubble, ESO, NASA, ESA
Videos: ESA/Hubble, ESO, NASA, ESA, M. Kornmesser
Interviews: ESA/Hubble, ESO, ESA
Music: Stellardrone
Web and technical support: Mathias Andre and Raquel Yumi Shida
Executive producer: Lars Lindberg Christensen
Animation of `Oumuamua outgassing
This animation, based on an artist’s impression, shows the first interstellar object `Oumuamua. Observations made with the NASA/ESA Hubble Space Telescope show that the object is moving faster than expected while hurtling towards the outer regions of the Solar System. Researchers assume that venting material from its surface due to solar heating is responsible for the observed speed. This outgassing can be seen in this animation as a subtle stream of material leaving the side of the object that is facing the distant Sun.
Credit:
ESA/Hubble, NASA, ESO, M. Kornmesser
Animation of `Oumuamua outgassing and rotating
This animation, based on an artist’s impression, shows the first interstellar object `Oumuamua. Hubble found `Oumuamua moving faster than expected. Researchers assume that venting material from its surface due to solar heating is responsible for the observed speed.
The animation also shows the tumbling motion of the object.
Credit:
ESA/Hubble, NASA, ESO, M. Kornmesser
Animation of `Oumuamua passing through the Solar System
This animation shows the path of the interstellar object `Oumuamua
through the Solar System. Unlike all other asteroids and comets observed
before, this body is not bound by gravity to the Sun. It has come from
interstellar space and will return there after its brief encounter with
our Solar System. Its hyperbolic orbit is highly inclined and it does
not appear to have come close to any other Solar System body on its way
in.
Credit:
Credit:
ESO, M. Kornmesser, L. Calcada. Music: Mylonite - MRP (Mylonite Recordz Production)
https://www.spacetelescope.org/videos/heic1813e/
Animation of `Oumuamua passing through the Solar System (annotated)
This animation (annotated) shows the path of the interstellar object
`Oumuamua through the Solar System. Unlike all other asteroids and
comets observed before, this body is not bound by gravity to the Sun. It
has come from interstellar space and will return there after its brief
encounter with our star system. Its hyperbolic orbit is highly inclined
and it does not appear to have come close to any other Solar System body
on its way in.
Credit:
Credit:
ESO, M. Kornmesser, L.Calcada. Music: Mylonite - MRP (Mylonite Recordz Production)
This animation shows the path of the interstellar object `Oumuamua through the Solar System. Recent measurements of `Oumuamuas flight path show that it is not moving as the laws of celestial mechanics predict — its course is slightly off.
Researchers assume that venting material from its surface due to solar heating is responsible for this behaviour. As outgassing is a behaviour typical for comets, the team thinks that `Oumuamua’s has to be classified as interstellar comet.
Credit:
NASA/JPL-Caltech
FUENTE: ESA/Hubble Information Centre
Animation showing the expected and measured trajectory of `Oumuamua
Researchers assume that venting material from its surface due to solar heating is responsible for this behaviour. As outgassing is a behaviour typical for comets, the team thinks that `Oumuamua’s has to be classified as interstellar comet.
Credit:
NASA/JPL-Caltech
FUENTE: ESA/Hubble Information Centre
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