Backyard Worlds was launched in February 2017 shortly before the 87th anniversary of the discovery of Pluto, which until its reclassification as a dwarf planet in 2006 was considered the Solar System's ninth major planet. Since that reclassification evidence has come to light that there may be another planet located in the outer region of the Solar System far beyond the Kuiper belt, most commonly referred to as Planet Nine. This hypothetical new planet would be located so far from the Sun that it would reflect only a very small amount of visible light, rendering it too faint to be detected in most astronomical surveys conducted to date. Models of the conjectured planet's atmosphere suggest however that methane condensation could in some cases make it detectable in infrared images captured by the Wide-field Infrared Survey Explorerspace telescope. Due to the effects of proper motion and parallax Planet Nine would appear to move in a distinctive way between images taken of the same patch of sky at different times. In addition to Planet Nine other objects such as nearby brown dwarfs would also be seen to move. The citizen scientists search through a flip book-style animation of specially processed infrared images captured by WISE, taken with filters at the wavelengths of 3.4 and 4.6 micrometers. The images contain instrumental artifacts and are noisy, which hampers the use of automated image processing software and makes the task ideal for exploiting human visual recognition capabilities. The project has been awarded a grant from NASA's Astrophysics Data Analysis Program which will fund it until 2020. In November 2018, the project was "rebooted", with new images and reduced noise.
Discoveries
In June 2017, it was announced that Backyard Worlds had made its first official discovery: a brown dwarf designated WISEA 1101+5400, of spectral type T5.5 and located 34 parsecs from Earth. A paper announcing the discovery was accepted for publication in Astrophysical Journal Letters, and Backyard Worlds now holds the record among all Zooniverse projects as having the shortest time from project launch to first publication. In December 2017, seven new brown dwarfs were confirmed, as well as two cool subdwarfs. The spectral types of the new brown dwarfs were T0, T2.8, T5, T6, T6.5, and two of type T8. In addition, there were 337 brown dwarf candidates awaiting spectra for confirmation. As of the first anniversary of the project in February 2018, the project had discovered 17 brown dwarfs and two cool subdwarfs. The coldest object discovered is of spectral type T9, which raises hopes of discovering type Y dwarfs in the future. In addition, a spectrum was also taken of one possibly variable object of unknown type that does not actually exhibit proper motion. There are 432 objects of interest awaiting verification, of which 38 are Y dwarf candidates. In July 2018 an update on the project's blog stated that in total 42 brown dwarfs had been spectroscopically confirmed from a list of 879 candidates. Fourteen of those confirmed are closer to the solar system than. In October 2018, a participant in the project discovered LSPM J0207+3331, the oldest and coldest known white dwarf to host a circumstellar disk despite being 3 billion years old. The disk consists of two rings at different temperatures. This star has been studied with the Keck telescope and is the object of ongoing research. As of July 2019, there are 1305 candidate objects to be followed up, of which there are 131 confirmed objects: 70 dwarfs of type T and 61 dwarfs of type L. Of the candidate and confirmed brown dwarfs, 55 of them are closer to the solar system than 20 parsecs. There are also roughly 100 Y dwarf candidates. At the 235th meeting of the American Astronomical Society in January 2020 the discovery of the wide brown dwarf binary W2150AB was presented by Jacqueline Faherty. The L1+T8 co-moving system is separated by 341 au. The system has the lowest gravitational binding energy for a brown dwarf binary that is not young and with the primary being a L-dwarf or later. The discovery of WISE J0830+2837, the first Y-dwarf discovered by volunteers was also presented at the 235th meeting by Daniella Bardalez Gagliuffi. The Y-dwarf was not detected by the Hubble Space Telescope, but the Spitzer Space Telescope did detect this object. It is about 11.2 parsec distant and has a temperature of about 350 K. A summary of the current status of the project was shown at the meeting. Those include 1503 L, T and Y dwarf candidates. At total there were 221 spectra taken.
