at separation of 1,000 AU and above, mean-
ing that if five to eight planets were living
in that range of parameters, some of them
should have been uncovered. Based on the
null result and the sensitivity reached for
each target, we inferred that less than 3% of
stars host a planet with a mass between 1 to
13 M Jup and a semi-major axis between 1,000
and 5,000 AU (95% confidence level).
How Weird Is It?
This work shows that giant planets around
young stars on very wide orbits are quite
rare. Some previous surveys have obtained
similar results, but WEIRD pushed the search
a little further out in orbital separation and
a little further down in planetary mass, still
returning a low occurrence rate. The low
frequency could be a clue toward a better
understanding of the formation process of
Jupiter-like objects on wide orbits. Indeed,
the results are probably telling us that they
don’t form in the same way as planets on
shorter orbits.
January 2019
One possibility is that the few known plan-
etary companions at large separations rep-
resent the low-mass tail end of the distribu-
tion of brown dwarf companions that form
like stars — rather than objects that form
like planets. Another possibility is that these
companions were once planets on short or-
bits that were pushed out following interac-
tions with other planets. A lot of questions
remain unanswered, and the search for exo-
planets on wide orbits continues.
Frédérique Baron is a PhD student at Univer-
sité de Montréal. The WEIRD survey was the
core of her PhD thesis. She can be reached at:
[email protected]
Étienne Artigau is a senior research associate at
Université de Montréal. He can be reached at:
[email protected]
David Lafrenière is a faculty member at Uni-
versité de Montréal. He can be reached at:
[email protected]
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