GeminiFocus January 2019 | Page 9

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] GeminiFocus 7