Backyard Worlds

Backyard Worlds: Planet 9

Type of site	Citizen science project
Available in	English
URL	www.backyardworlds.org
Commercial	No
Registration	Optional
Launched	15 February 2017; 7 years ago (2017-02-15)
Current status	Online

Backyard Worlds: Planet 9 is a

Backyard Worlds was launched in February 2017, shortly before the 87th anniversary of the discovery of Pluto,^[3] 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.^[4][1] However, models of the conjectured planet's atmosphere suggest that methane condensation could in some cases make it detectable in infrared images captured by the Wide-field Infrared Survey Explorer (WISE) space telescope.^[5] 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 of interest – such as undiscovered nearby brown dwarfs – would also be seen to move in the project's images.

Project description

Citizen scientists accessing the website search through a

Once candidates have been identified the science team follow-up the most scientifically interesting objects using ground-based telescopes (at sites such as Mont Mégantic Observatory, Apache Point Observatory, W. M. Keck Observatory, Las Campanas Observatory, Gemini Observatory and the NASA Infrared Telescope Facility) and space telescopes (principally the Spitzer Space Telescope and the Hubble Space Telescope), in order to clarify their nature and assign a spectral type if possible.

The project has been awarded a grant from NASA's Astrophysics Data Analysis Program which will fund it until 2020.^[9]

In November 2018, the project was "rebooted", with new images and reduced noise.^[10] By August 2020, more than 100,000 citizen scientists worldwide had taken part in the project.^[11]

Cool Neighbors project

In June 2023 the project "Backyard Worlds: Cool Neighbors" was launched.^[12] The "Planet 9" predecessor was focused on finding a hypothesised outer planet, which is not ideal in finding faint brown dwarfs. The new project has switched to focus on searching for faint and cool Y-dwarfs. The new "Cool Neighbors" project pre-selects its images with the help of machine learning.^[13]

Project status

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.^[14]

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.^[9]

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 20 parsecs (65 light-years).^[15]

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.^[16]

At the 235th meeting of the American Astronomical Society in January 2020 a summary of the current status of the project was presented and this included 1503 L, T and Y dwarf candidates. In total 221 spectra have been taken of candidate objects.^[17]

Published discoveries

WISEA 1101+5400

In June 2017, it was announced that Backyard Worlds had made its first official discovery: a brown dwarf designated

In October 2018, a participant in the project discovered LSPM J0207+3331 – the oldest and coldest white dwarf known to host a circumstellar disk, despite being 3 billion years old. The time since this star became a white dwarf is far longer than the expected timescale for such disks to be cleared from a system. The disk consists of two rings at different temperatures. This star has been studied with the Keck telescope and is the subject of ongoing research.^[19][20]

W2150AB

A study by Lodieu et al.[27] observed WISE1810 with a range of ground-based telescopes, using imaging and spectroscopy. They find a closer distance of 8.9+0.7
−0.6 parsec, a radius of 0.67+0.32
−0.20 R_J and a mass of 17+56
−12 M_J. This makes WISE1810 the closest extreme ultra-cool subdwarf and the closest extreme metal-poor brown dwarf known to science, as of June 2022. The optical and infrared spectrum does not show any methane or carbon monoxide absorption, which is expected at these temperatures of about 800 K, and the WISE photometry suggest a depleted methane atmosphere. Only H₂ CIA and water vapor absorption is detected, suggesting a carbon-deficient and metal-poor atmosphere, or alternatively an oxygen-enhanced atmosphere.

95 cold brown dwarfs observed with Spitzer

In August 2020, the Backyard Worlds team published a paper in the Astrophysical Journal detailing follow-up conducted using the Spitzer Space Telescope on a sample of the coldest discoveries that had been made before the telescope was decommissioned. 95 had Spitzer mid-infrared colors consistent with being a cold brown dwarf, with 75 of these having their proper motion confirmed by comparison to their position in WISE images. Among the discoveries highlighted as most significant were; 3 possible T subdwarfs based on high tangential velocity estimates, a rare widely-separated T8 companion to the white dwarf LSPM J0055+5948, and 5 new Y dwarfs, four of which (including the previously published WISE J0830+2837) where Spitzer colors indicate they have spectral types Y1 or later, with only at most 6 of these coldest set of brown dwarfs previously being known. The T8 companion to the white dwarf LSPM J0055+5948 could be the oldest (7-13 billion years old) brown dwarf known to science, together with Wolf 1130C (>10 billion years old).^[8]

Co-moving benchmark systems

The backyard worlds project found additonal co-moving systems. 34 low-mass co-moving companions were discovered in 2022 with the NOIRLab Source Catalog DR2.^[28] Later in March 2024 an additional 89 ultracool dwarf companions were identified. This study increased the number of ultracool companions to FGK stars by about 42%. These benchmark system represent a wide variety of systems, including six systems with white dwarf hosts, systems with binary hosts or companions that are binaries, systems with old or young ages, systems with red or blue spectral types and systems with a wide separation of >1000 astronomical units (AU). One candidate young co-moving system is compromised of GJ 900, a K7+M4+M6 triple star system and the T9-dwarf CW2335+0142, which could be a planetary-mass object (~10.5 M_J), if it is confirmed to be part of the system. Another notable system is CW0627−0028AB, which is a wide T0blue+T3 dwarf system or a possible triple (L5+T2.5)+T3 system. If the distance is confirmed, it would be the widest substellar binary discovered at a separation of about 860 AU. The brown dwarf companion CWISE J060202.17-462447.8 (~52 M_J) to the white dwarf WD J060159.98-462534.40 is an additional contender for the oldest brown dwarf with an age of 10.9+2.6
−2.0 billion years.^[29] Additional M+T co-moving systems were discovered in April 2024 in a collaborative work together with the CatWISE team. 13 new systems were discovered, representing a 60% increase of the number of M+T systems. The sample includes young and old objects, including the candidate planetary-mass companion 2MASS J05581644–4501559 B and UCAC3 52–1038 B, which is on a wide 7100 AU orbit.^[30]

Additional discoveries

This list contains additional notable discoveries by the Backyard Worlds: Planet 9 project.

Name	ly )	Spectral type	Mass (MJ)	Temperature K (°C)	note	Ref
WISEA 1930−2059	30.7+1.5 −1.4	> Y1		367±79 (94)	Cold and nearby Y-dwarf candidate	[8][31]
WISEU 0503−5648	33.2+1.4 −1.3	>Y1		367±79 (94)	Target for JWST follow-up observations	[8][32][31]
CWISE J2035–4936	265.8±4.9	M8pec			Companion to a red dwarf, underluminous and peculiar spectrum	[33]
2MASS J13173072+4833343	127.2±0.3	M8.5	80.2+0.5 −1.8		Orbits a white dwarf at 79 au. The white dwarf has an estimated age of about 5.5 Billion years.	[34]
CWISE 0738−6643	142.2+33.9 −27.4	esd(?) T5 ±1.2			candidate extreme subdwarf of spectral type T	[35]
WISEA 1553+6933	125.9+15.0 −13.7	sdT4±0.5		1076±89 (803)	confirmed subdwarf of spectral type T, might be kinematically extreme	[35]
CWISE 2217−1454	128.5+31.0 −24.8	esd(?)T5.5±1.2			candidate extreme subdwarf of spectral type T	[35]
WISE 1534−1043	53.2+4.6 −3.9	sdY?		<500 (<227)	Likely first subdwarf of spectral type Y, extreme blue color with Spitzer ch1-ch2, while very red in J-ch2	[36]
HP Draconis C	260.9±1.6		471.3±31.4	7087±205 (6814)	White dwarf, separated by 1140 au from the eclipsing binary HP Draconis	[37]
Ross 19 B	56.9	T9.5±1.5	15 - 40	500+115 −100 (227)	Orbits the metal-poor and old (~7.2 Billion years) red dwarf Ross 19 A with a projected distance of 9900 au. The pair has a very low gravitational binding energy, between ${\displaystyle 4.8\times 10^{39}}$ and ${\displaystyle 3.0\times 10^{40}}$ ergs, near the theoretical minimum of 1040 ergs for substellar binaries.	[38]
CWISE 0617+1945 AB	28.2±5.7	L2+L4		1853+40 −52 (1580)	nearby brown dwarf binary co-discovered by Backyard Worlds volunteers	[31][39]
2MASS J22410186-4500298	189.2±6.5	L2			Forms with LEHPM 5005 a co-moving system. LEHPM is reported in the discovery as a possible M-dwarf binary.	[40]
BD+60 1417b	144±13	L8γ	10-20	1303±74	Confirmed exoplanet[41] orbiting around a young K0 star, with a projected separation of 1662 astronomical units.	[42]
CWISE J052306.42-015355.4	≤222	esdT(?)			extreme T subdwarf candidate	[43]
CWISE J0146-0508AB	~130	L4+L8(blue)	72±6; 66±10	1720±150; 1340±140	The widest known (as of Feb 2022) brown dwarf binary not in a star cluster or stellar association. The pair has a projected separation of 129 astronomical units.	[44]
CWISE J0506+0738	104	L8γ-T0γ	7 ± 2	1140 ± 80	Candidate of the Beta Pictoris Moving Group. Very red near-infrared colors.	[45]
W0727−3607	111	L7+T4			Candidate spectroscopic binary, or a single highly variable object	[46]
W1036−5144	88	L7+T4			Candidate spectroscopic binary	[46]
W1344−7320	65	L7+T7			Candidate spectroscopic binary	[46]
W1055+5443	19.5-26	Y0pec		500±150	Bluest Spitzer colors amog spectroscopically confirmed Y-dwarfs. Discovered by Caselden (BYW, CatWISE), Goodman (BYW) and Kirkpatrick (CatWISE)[31]	[47]

See also

• Amateur astronomy
• Citizen science

Zooniverse projects:

References