Space and Physics

Update On Oumuamua: Interstellar Visitor May Mean Neptune-Like Planets Are Common


Stephen Luntz

Freelance Writer

clockJan 23 2018, 13:09 UTC

An artist's impression of Oumuamua. We'll never know exactly what it looks like but deeper analysis of the observations we collected support this impression. ESO/M.Kornmesser

In October last year, astronomers were thrilled to witness the passage of an interstellar object through the Solar System for the first time. Oumuamua is now too far gone for new observations, but we will be processing what we saw for a long time. A collection of papers in progress have provided exciting, if speculative, deductions about the cosmic visitor.


Since we've never seen anything like Oumuamua before, it is easy to assume such visits must be very rare. However, we have only recently started scanning the skies with sufficient coverage and sensitivity to make detection of such an object likely.

If you enter a weekly lottery and win after only a few tries, you might just have been lucky, but it is more likely the odds are not all that long. Yale University's Professor Gregory Laughlin has used this principle to estimate the number of objects passing through the inner Solar System, and therefore their frequency in the galaxy (if it was not a fluke we happened to see one already).

His conclusion, published in Research Notes of the AAS, is that there are 2x1026 interstellar objects whizzing around the galaxy, with a combined mass roughly 100 billion times that of Earth.

For an object to be given enough gravitational heft to be thrown from its solar system, it needs to encounter a large planet. Moreover, the closer such an encounter occurs to the star, the more massive the planet needs to be to do the throwing. Most planets we have discovered around other stars are either too small (super-Earths) or too close to the star (hot Jupiters) to be responsible.


Laughlin thinks most Oumuamua-like objects must have been sent on their way by planets at least 5 astronomical units (AU) from stars with masses similar to the Sun, or 1 AU for a red dwarf. If so, and they are as common as he suspects, there must be a lot of planets of Neptune-like mass lurking in the outer reaches of their star systems where we have little chance of detecting them using current methods. Laughlin is a proponent of planet nine, a local equivalent.

Mass and orbital distance of planets we have found around other stars. If Oumuamuas are common there must be many more planets in the top right than we have yet found. Laughlin and Batygin

Research Notes of the AAS is a newly revived project where astronomers post short works that may eventually be turned into full papers but are yet to be peer-reviewed.

Other notes confirm Oumuamua could not have come from our Solar System and is unlikely to have originated around any nearby star, despite speculation of possible sources. One of Oumuamua's distinctive features was its ratio of length to width, estimated as being around 10. We haven't seen it precisely enough to get an exact ratio, but confirmation of a minimum of 5.3 demonstrates this is a very unusual object.

Space and Physics
  • Planet Nine,

  • oumuamua,

  • interstellar visitor,

  • Neptune-like planets