Unexpected Excess of Giant Planets in Star Cluster Messier 67

[Judi Lynn]

Unexpected Excess of Giant Planets in Star Cluster Messier 67
European Southern Observatory - ESO
June 17, 2016


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This artist's impression shows a hot Jupiter planet orbiting close to one of the stars in the rich old star cluster Messier 67, in the constellation of Cancer (The Crab). Astronomers have found far more planets like this in the cluster than expected. This surprise result was obtained using a number of telescopes and instruments, among them the HARPS spectrograph at ESO's La Silla Observatory in Chile. The denser environment in a cluster will cause more frequent interactions between planets and nearby stars, which may explain the excess of hot Jupiters.

Credit: ESO/L. Calçada
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An international team of astronomers have found that there are far more planets of the hot Jupiter type than expected in a cluster of stars called Messier 67. This surprising result was obtained using a number of telescopes and instruments, among them the HARPS spectrograph at ESO's La Silla Observatory in Chile. The denser environment in a cluster will cause more frequent interactions between planets and nearby stars, which may explain the excess of hot Jupiters.

A Chilean, Brazilian and European team led by Roberto Saglia at the Max-Planck-Institut für extraterrestrische Physik, in Garching, Germany, and Luca Pasquini at ESO, has spent several years collecting high-precision measurements of 88 stars in Messier 67 [1]. This open star cluster is about the same age as the Sun and it is thought that the Solar System arose in a similarly dense environment [2].

The team used HARPS, along with other instruments [3], to look for the signatures of giant planets on short-period orbits, hoping to see the tell-tale "wobble" of a star caused by the presence of a massive object in a close orbit, a kind of planet known as a hot Jupiters. This hot Jupiter signature has now been found for a total of three stars in the cluster alongside earlier evidence for several other planets.

A hot Jupiter is a giant exoplanet with a mass of more than about a third of Jupiter's mass. They are "hot" because they are orbiting close to their parent stars, as indicated by an orbital period (their "year&quot that is less than ten days in duration. That is very different from the Jupiter we are familiar with in our own Solar System, which has a year lasting around 12 Earth- years and is much colder than the Earth [4].

More:
https://www.sciencedaily.com/releases/2016/06/160617082530.htm

[longship]

1. Of course there is selection bias.

Our methods of discovering planets are highly biased towards large, close-in planets (the larger and more closer-in, the better). We see a lot of them because they are the easiest to see. Earth-like planets at Earth-like distances from Sol-like stars are really, really difficult to detect. That's why we haven't detected any.

Our data is biased by how we detect extra solar planets, the only ways we can do it.

The best effort was the Kepler space telescope whose sole purpose was to find out how many Earth-like planets exist in the galaxy by staring at about 150,000 stars continuously measuring their light output in case a planet crossed in front. Unfortunately the reaction wheels which kept it pointed precisely at those stars failed just at the point in the mission where an Earth-sized planet at an Earth-like distance from a Sol-sized star could be discovered.

Regardless, Kepler gathered enough data to state that there are likely many billions of Earth-like planets in the Milky Way, upwards of 40 billion. That, in spite of the technical failures.

Just remember, gathering this data had some rather severe selection bias. We discover lots of large, close-in planets because they the easiest to discover.