1I / 'Oumuamua

from Wikipedia, the free encyclopedia
1I / ʻOumuamua [i]
Image taken with the William Herschel telescope. 1I / ʻOumuamua is the point in the center of the picture. Because of the rapid movement of the interstellar object, the background stars appear as streaks of light.
Image taken with the William Herschel telescope . 1I / ʻOumuamua is the point in the center of the picture. Because of the rapid movement of the interstellar object, the background stars appear as streaks of light.
Properties of the orbit ( animation )
Epoch:  October 31, 2017 ( JD 2,458,057.5)
Orbit type hyperbolic
Numerical eccentricity 1.1995
Perihelion 0.2553 AU
Inclination of the orbit plane 122.686 °
Perihelion September 9, 2017
Physical properties of the core
Medium diameter effective about 200 m
assuming an albedo of 0.04
Dimensions (cigar-shaped) → Phys. Own.
history
Explorer Pan-STARRS
Date of discovery 19th October 2017
Older name 1I / 2017 U1, A / 2017 U1, C / 2017 U1 (PANSTARRS)
Source: Unless otherwise stated, the data comes from JPL Small-Body Database Browser . Please also note the note on comet articles .

1I / ʻOumuamua (previously A / 2017 U1 and C / 2017 U1 (PANSTARRS) , pronunciation  [ ʔoʊˈmuːəˈmuːə ] ) is the first object observed within the solar system that was classified as interstellar . Please click to listen!Play

discovery

The object was discovered by the Pan-STARRS telescope in Hawaii on October 19, 2017 , when it had already flown past the sun and was on its way back to interstellar space. The object had already passed Earth at a distance of around 15 million kilometers five days earlier. At the time of discovery, the object was already about 33 million kilometers away from the earth, which is about 85 times the distance between the moon and the earth, or about a fifth of the distance between the earth and the sun .

Due to its orbital properties, it was originally thought to be a comet . When, on closer observation, no tail or coma was observed, the object was classified as an asteroid about a week later . At the end of June 2018, ʻOumuamua was again classified as a comet after a detailed analysis of its trajectory, which suggests a loss of mass.

Trajectory

The orbit of A / 2017 U1 in the inner solar system
The time window of 'Oumuamua's approach to the sun

'Oumuamua flew nearly perpendicular to the track planes one of the planets in the solar system. On September 2, 2017, he crossed the ecliptic plane between the Sun and Mercury . Back calculations showed a direction of origin from the constellation Lyra , not far from its main star Vega . It should be noted, however, that the Vega was not where it is now because of its spatial movement about 300,000 years ago. Relative to the local rest system , the sun flies at around 20 km / s in the direction of the sun apex . The sun apex is also the approximate direction from which 'Oumuamua was coming towards you at about 6 km / s, which added up to a speed of about 26 km / s.

On September 9, 2017, the object passed the apex of its career at a top speed of 87.3 kilometers per second and the shortest distance of 37.6 million kilometers from the sun.

On October 14, 2017, 'Oumuamua flew past Earth at a closest distance of about 15 million kilometers, which is about 60 times as far as the moon . The object is now moving with slowly decreasing speed towards the constellation Pegasus and will leave the solar system on its orbit again.

'Oumuamua has an orbital eccentricity of about e = 1.2, so its orbit is hyperbolic .

During further observations of the trajectory of the object through various earth-based telescopes and the Hubble space telescope , an orbit deflection could be observed. The deceleration of the body when it moves away from the sun takes place a tiny bit less than it would have to be under the pure influence of gravity . As a possible cause of the additional acceleration was outgassing of volatile components due to the sun called proximity. Roman Rafikov countered that outgassing would probably have led to a significant change in the rotation, which could not have been detected.

Physical Properties

The apparent magnitude of ʻOumuamua between 2015 and 2020

For further identification, ʻOumuamua was observed with several telescopes, including Pan-STARRS1, the Canada-France-Hawaii Telescope , the Gemini-South Observatory , the Very Large Telescope , the United Kingdom Infrared Telescope and the Keck Observatory .

The exceptionally strong fluctuations in brightness with periods of 6.9 to 8.3 hours suggest a cigar-shaped object with an axis ratio of more than 5: 1 for the two largest axes. In an evaluation of all available photometric observation data , no rotation period could be found that could adequately explain the observed fluctuations in brightness. ʻOumuamua probably does not rotate around one of its main axes , but moves staggering through space . It is likely that it already left its original planetary system in this state . It will take at least a billion years to dampen the irregular rotation through internal friction , and possibly considerably longer. The unusual shape fueled speculation that it could be an alien spaceship .

No dust could be found near the object, from which it is concluded that ʻOumuamua does not contain water and is made of rock or metal. Since its surface has presumably become dark due to the billions of years of continuous bombardment with cosmic rays , it is assumed that the albedo is low . A typical value of 0.04 for inactive asteroids results in a mean radius of (102 ± 4) m. An exact estimate of the size is difficult and depends on various assumptions. Depending on the assumed albedo, internal tensile strength , axis of rotation and density , different dimensions result (the dimensions are rough approximations, the shape is assumed to be an ellipsoid ):

  • In the event that 'Oumuamua rotates around its shortest axis, it must be held together by an internal tension . A rubble pile or a double asteroid would be excluded. Assuming a value of 0.04 for the albedo results in the dimensions 800 m × 80 m × 80 m, with a value of 0.2 it would be 360 ​​m × 36 m × 36 m.
  • In the event that 'Oumuamua rotates around its longest axis (a rotation around the central axis would be unstable), at a density of more than 1500 kg / m³ it could only be held together by its own gravity. For an albedo of 0.04 this results in dimensions of around 360 m × 180 m × 18 m, with a value of 0.2 it would be 160 m × 80 m × 8 m.

Its surface is reddish in color, like the surface of comets, D-type asteroids and other objects in the outer solar system . The color is attributed to the presence of organic substances. Color changes in the observed light curves suggest a varying surface texture with a predominantly color-neutral region and a large red area.

Variation in the brightness of ʻOumuamua, observed on three days in October 2017. The large range of fluctuations can be explained by a very elongated shape and a tumbling rotation. The different colored points represent measurements through different filters in the visible and near-infrared part of the light spectrum. The dashed line shows the light curve expected for an ellipsoid with an axis ratio of 1: 1: 10. Deviations from this line indicate an irregular shape or albedo of the object.

In November 2018 Shmuel Bialy and Abraham Loeb came to the conclusion that the observed non-gravitational deviation in orbit without observable dust formation can be explained well by an extremely thin object (approx. 0.3-0.9 mm) with a large area that is affected by the radiation pressure of the Sunlight is pushed off its course. They speculated that it could be a solar sail that came from an alien civilization.

origin

Animated trajectory of ʻOumuamua

The exact origin of the interstellar object cannot yet be determined, especially since its trajectory shows non-gravitational influences.

According to a publication immediately after the discovery, using the orbital data of ʻOumuamua before the encounter with the sun, it could be ruled out with high probability that the interstellar object from one of the star systems is closer than 11 light years or from the Luhman-16 system. If one of the motion vectors 1481 stars at a distance to 25 Parsec from the extended catalog Hipparcos XHIP a median forms, one obtains an estimate of the average motion of the stars in the vicinity of the sun, the local rest system (LSR). The movement of 'Oumuamua before the encounter with the sun comes very close to this median vector of the LSR. It is particularly close to the mean movement of a group of relatively close red dwarfs . Compared to the local rest system, there is no significant movement in the radial or vertical direction in relation to the Milky Way .

The head of the Astronomical Institute at Harvard University , Avi Loeb , does not rule out that the object could be an active space probe . In a study published in the journal Nature in July 2019 , a team of scientists postulates that 'Oumuamua is an object of natural origin.

designation

On November 6, 2017, the Minor Planet Center confirmed the new designation 1I / ʻOumuamua . This is a newly introduced classification for this object in the nomenclature of asteroids and comets. The capital letter "I" as the second character in the name stands for interstellar object . The leading number 1 in front of it counts the object as the first found of the mentioned category. According to the Minor Planet Center, the designations 1I , 1I / 2017 U1 and 1I / 2017 U1 (ʻOumuamua) are also correct. ʻOumuamua means something like "reach first" in Hawaiian . This should allude to his quality as a “messenger” from a distant past. Previously, in the scheme of the previous designation, the object was provisionally designated as A / 2017 U1 or, when it was initially mistaken for a comet, as C / 2017 U1 (PANSTARRS) .

Search for radio signals of artificial origin

The Green Bank Telescope

In mid-December 2017, as part of the Breakthrough Listen research project, the radio telescope at the Green Bank Observatory in the US state of West Virginia was aimed at ʻOumuamua in order to receive possible signals of artificial origin from 'Oumuamua. It is extremely unlikely that signals from aliens will actually be received, but due to the previously unique opportunity, the measurements were worth a try. In four observation blocks of two hours each in the L , S , C and X bands , data were collected over two weeks. No evidence of artificial signals or a cometary coma was found.

SETI had already carried out a similar investigation with the Allen Telescope Array in California , but had not found anything.

reachability

Because of the high hyperbolic excess speed of about 26.3 km / s, ʻOumuamua is difficult to reach for spacecraft. The spacecraft with the currently highest hyperbolic excess speed is Voyager 1 with approx. 16.6 km / s. Two studies by the British Initiative for Interstellar Studies came to the conclusion that missions to ʻOumuamua with today's technologies are possible within a start time window from 2021 to after 2047. One mission concept is based on a combined Jupiter flyby and Sonnen- Oberth maneuver . The Jupiter flyby maneuver would therefore bring the probe on a trajectory in the direction of the sun. A solid motor would be ignited in the perihelion and catapulted the probe out of the solar system. The calculations showed that with this maneuver, ʻOumuamua could be reached within 16 to 17 years of takeoff. This would require a powerful launch vehicle ( Falcon Heavy , Space Launch System ), solid fuel motors and a heat shield similar to that of the Parker Solar Probe . The feasibility of such a combination of maneuvers with today's technologies was previously examined by a study by the Keck Institute of Space Studies at the California Institute of Technology . An older study by researchers at Yale University had already come to the result that objects similar to 'Oumuamua can be reached with today's technologies.

Other objects on hyperbolic orbits

The comet 2I / Borisov , discovered in August 2019, has an orbital eccentricity of 3.4 and is the second interstellar object observed in the solar system .

We also know some comets in the solar system whose orbital eccentricities are greater than 1.0, for example comet C / 1980 E1 (Bowell) , which has an orbital eccentricity of 1.0577. This comet came from the Oort cloud into the interior of our solar system. Its orbit was diverted to a hyperbolic orbit during its nearby Jupiter passage . The space probes Pioneer 10 , Pioneer 11 , Voyager 1 , Voyager 2 and New Horizons are also on hyperbolic orbits. The probes reached the third cosmic speed ( ) by swing-by maneuvers on Jupiter and Saturn.

See also

literature

  • Alan P. Jackson et al .: Ejection of rocky and icy material from binary star systems: Implications for the origin and composition of 1I / 'Oumuamua. In: Monthly Notices of the Royal Astronomical Society: Letters. sly033, March 19, 2018, doi: 10.1093 / mnrasl / sly033

Web links

Commons : 1I / ʻOumuamua  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d e f g Karen J. Meech, Robert Weryk, Marco Micheli, Jan T. Kleyna , Olivier R. Hainaut, Robert Jedicke, Richard J. Wainscoat, Kenneth C. Chambers, Jacqueline V. Keane, Andreea Petric, Larry Denneau, Eugene Magnier, Travis Berger, Mark E. Huber, Heather Flewelling, Chris Waters, Eva Schunova-Lilly, Serge Chastel: A brief visit from a red and extremely elongated interstellar asteroid . In: Nature . November 20, 2017, doi : 10.1038 / nature25020 .
  2. ↑ Ken Croswell: Astronomers race to learn from first interstellar asteroid ever seen . Nature News on nature.com from October 31, 2017, doi: 10.1038 / nature.2017.22925 .
  3. ^ Carlos de la Fuente Marcos, Raul de la Fuente Marcos: Pole, pericenter and nodes of the interstellar minor body A / 2017 U1. In: Research Notes of the AAS. November 1, 2017, Volume 1, No. 1, doi: 10.3847 / 2515-5172 / aa96b4 .
  4. ↑ JPL: Small Asteroid or Comet 'Visits' from Beyond the Solar System. In: jpl.nasa.gov. Jet Propulsion Laboratory California Institute of Technology , October 27, 2017, accessed October 27, 2017 .
  5. ↑ a b c Marco Micheli, Davide Farnocchia, Karen J. Meech, Marc W. Buie , Olivier R. Hainaut: Non-gravitational acceleration in the trajectory of 1I / 2017 U1 ('Oumuamua) . In: Nature . June 27, 2018, doi : 10.1038 / s41586-018-0254-4 .
  6. ^ Tilmann Althaus: The first interstellar visitor? In: Spektrum.de . Spektrum der Wissenschaft Verlagsgesellschaft , October 26, 2017, accessed on October 27, 2017 .
  7. ↑ Interstellar Asteroid FAQs. November 20, 2017. Retrieved November 23, 2017 .
  8. ↑ Julia Merlot: Researchers see interstellar objects. In: Spiegel.de . October 27, 2017. Retrieved October 27, 2017 .
  9. ↑ Roman R. Rafikov: Spin Evolution and cometary interpretation of the Interstellar Minor Object 1I / 2017 'Oumuamua. The Astrophysical Journal Letters 867, 2018, doi: 10.3847 / 2041-8213 / aae977 (free full text).
  10. ^ A b Wesley C. Fraser, Petr Pravec , Alan Fitzsimmons , Pedro Lacerda, Michele T. Bannister: The tumbling rotational state of 1I / 'Oumuamua . In: Nature Astronomy . February 9, 2018, ISSN  2397-3366 , doi : 10.1038 / s41550-018-0398-z .
  11. ↑ a b Mike Wall: Interstellar Visitor Stays Silent - for Now, No Signs of Aliens on ʻOumuamua. In: Scientific American . December 14, 2017, accessed December 15, 2017 .
  12. ↑ Jan Dönges: Interstellar visitor: 'Oumuamua in truth an extraterrestrial solar sail? In: Spektrum.de. November 6, 2018, accessed November 6, 2018 .
  13. ↑ Eric Mamajek: Kinematics of the Interstellar Vagabond A / 2017 U1. (PDF) In: arxiv : 1710.11364 . October 31, 2017, accessed November 2, 2017 .
  14. ↑ Andreas Müller: What the "alien spaceship" 'Oumuamua is all about. Retrieved January 5, 2019 .
  15. ↑ Michele T. Bannister, Asmita Bhandare, Piotr A. Dybczyński, Alan Fitzsimmons, Aurélie Guilbert-Lepoutre: The natural history of 'Oumuamua . In: Nature Astronomy . tape 3 , no. 7 , July 2019, ISSN  2397-3366 , p. 594–602 , doi : 10.1038 / s41550-019-0816-x ( nature.com [accessed July 18, 2019]).
  16. ^ Robert Naeye: The first known interstellar interloper. In: Astronomy.com. November 7, 2011, accessed November 7, 2017 .
  17. ↑ Gareth V. Williams: MPEC 2017-V17: NEW DESIGNATION SCHEME FOR INTERSTELLAR OBJECTS. In: Minor Planet Center . November 6, 2017, accessed November 7, 2017 .
  18. ^ J. Emilio Enriquez, Andrew Siemion, T. Joseph W. Lazio, Matt Lebofsky, David HE MacMahon, Ryan S. Park, Steve Croft, David DeBoer, Nectaria Gizani, Vishal Gajjar, Greg Hellbourg, Howard Isaacson, Danny C. Price : Breakthrough Listen Observations of 1I / 'Oumuamua with the GBT . In: Research Notes of the AAS . tape 2 , no. 1 , January 15, 2018, ISSN  2515-5172 , p. 9 , doi : 10.3847 / 2515-5172 / aaa6c9 .
  19. ^ Sarah Lewin: Breakthrough Listen Is Eavesdropping on Strange Interstellar Object ʻOumuamua. In: Space.com. December 11, 2017, accessed December 15, 2017 .
  20. ↑ a b c d Andreas M. Hein, Nikolaos Perakis, T. Marshall Eubanks, Adam Hibberd, Adam Crowl, Kieran Hayward, Robert G. Kennedy III, Richard Osborne: Project Lyra: Sending a spacecraft to 1I / 'Oumuamua (former A / 2017 U1), the interstellar asteroid . In: Acta Astronautica . in press, January 7, 2019. arxiv : 1711.03155 .
  21. ^ A b Adam Hibberd, Hein Andreas M., T. Marshall Eubanks: Project Lyra: Catching 1I / 'Oumuamua - Mission Opportunities After 2024 . In: arXiv . February 14, 2019. arxiv : 1902.04935 .
  22. ↑ EC Stone, Leon Alkalai, Louis Freedman: Science and Technology Steps Into the Interstellar Medium . 2015.
  23. ^ Darryl Seligman, Gregory Laughlin: The Feasibility and Benefits of in situ Exploration of Oumuamua-like Objects . In: The Astronomical Journal . 155, No. 5, April 12, 2018, p. 217. arxiv : 1803.07022v2 . doi : 10.3847 / 1538-3881 / aabd37 .
  24. ↑ C / 1980 E1 (Bowell) in the Small-Body Database of the Jet Propulsion Laboratory ., Accessed on November 7, 2017.
  25. ↑ Michael F. Ahearn, DG Schleicher, RL Millis, PD Feldman, DT Thompson: Comet Bowell 1980b. In: Astronomical Journal . No. 89 , 1984, pp. 579-591 , doi : 10.1086 / 113552 , bibcode : 1984AJ ..... 89..579A (English).