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BROWN DWARFS were once the most exciting thing to extrasolar planet seekers, as it seemed our technology would detect these large objects in advance of smaller planets like the ones orbiting our own sun. Now, brown dwarfs have disappeared from the spotlight and are rarely mentioned in our popular history of exoplanet discoveries. What happened? Well, it seems the vanishing act of Van Biesbroeck 8b had a lot to do with it....

These days, it is a well-advertised fact that the first planet discovered around a star outside our solar system is 51 Pegasi b. This "hot jupiter" was first detected by two European astronomers in 1995, and quickly confirmed by Geoff Marcy and Paul Butler, who went on to pull many more hot jupiter exoplanet discoveries out of the data they had been collecting for years. Out came 70 Virginis b, 47 Ursae Majoris b, and the hunt for exoplanets shifted into high gear and a respectable place in the spotlight of astronomy.

The common footnote to this story is that Mankind did detect pulsar planets prior to this in 1992, using very different methods and yielding a result that was both unexpected and not really understood. Such planets orbiting pulsars have proven extremely rare so far, with barely 4 or 5 discovered compared to the hundreds of regular exoplanets known to exist today.

But perhaps there's one more footnote missing from this history. Before the common hot jupiter exoplanets made news, before the pulsar planets were detected, astronomers had been excited about something else orbiting stars other than our own. These were called Brown Dwarfs, a type of object that was something between a small cold red dwarf star and a really big Jupiter-like planet.

Even today in 2015, scientists are fiercely debating whether brown dwarfs should be officially designated as stars, or planets, or neither. Brown dwarfs are typically hot and dense, but not enough to begin to fuse hydrogen, burn, and emit light as a star does. Does that make them planets? Back in 1993, before the hot jupiter craze in the exoplanet hunting field, brown dwarfs were all the rage.

And perhaps even that was an extension of our interest in discovering that some stars were actually two stars orbiting each other - a binary system, or three stars orbiting each other - a trinary system. Our hunt for objects in the sky just keeps getting more refined, as we progress from the big, bright, and obvious, to the small, dim, and obscure.

John Grayson Jr.'s 1993 book "Extraterrestrial Life" contains a chapter entitled "Planets of Other Stars", in which brown dwarfs were generally referred to as planets, although the debate concerning such a title was mentioned, as was the discovery of the pulsar planets. Many then-recently discovered brown dwarfs are detailed in this chapter in similar fashion to the way we get excited about hot jupiters and smaller exoplanets today.

According to Grayson, the now infamous star-wobble technique was theoretically able to detect planets long before any were confirmed. One of our nearest neighbours in space, Barnard's Star, was one of the early subjects for planetary searches, and as early as 1963, astronomer Peter Van de Kamp announced detection of a planetary system there. The main companion was calculated to be massive - a type now known as a brown dwarf. But were they detecting one planet, or two? And how many other planets might be in the system? The accuracy of the data at the time was not enough to know exactly what they had.

Even so, the excitement generated from this led to similar speculation about Epsilon Eridani and 70 Ophiuchi A, which could not be confirmed with confidence at the time. Theories of planetary formation also became further refined, as disc-shaped nebulas of accreting matter were detected around bright young stars such as Vega and Beta Pictoris.

The term "brown dwarf" was coined in the mid-1970's by Jill Tarter in one of her scientific papers, and the name caught on. Astronomers began to believe that these objects were in a category of their own, separate from planets and stars. Grayson makes a case for why he considers all gas giants (including Jupiter, Saturn, Uranus, and Neptune) to be brown dwarfs, and all brown dwarfs to be planets.

This brings us to the very curious object of Van Biesbroeck 8b, discovered in December 1984. Perhaps because it was detected via both the wobble of its parent star and a strong infrared emission of its own, it was thought to be a more conclusive discovery than any other previous brown dwarf. According to Grayson, "the existence of the first extrasolar planet was announced." The parent star Van Biesbroeck 8 is a red dwarf in the constellation of Ophiuchus. At a distance of only 21 light years, it is one of the nearest stars in the heavens to our own sun. The orbiting brown dwarf / planet Van Biesbroeck 8b was estimated to be between 30 to 45 times the mass of Jupiter - a significant difference, but not enough for it to qualify as a star or a protostar. At an estimated temperature of 1000 degrees Celsius, it proved to be very bright in infrared wavelengths, even while not bright at all in visible light.

However, the story of Van Biesbroeck 8b takes a bizarre twist. Despite originally being confirmed twice, it has since disappeared, and modern astronomers are unable to find it. This sheds doubt upon the original discovery. Were there errors in the original observations? Did this brown dwarf ever truly exist at all?

It should be noted that its parent star, Van Biesbroeck 8, is part of a quintuple star system - in other words, 5 red dwarf stars all gravitationally tied together and orbiting each other. Potentially, this could introduce complications into the orbits of any other less noticeable components of the system, complications that we simply don't yet understand. Dark Matter? Dark Energy? Hmmm.

We should also note that astronomers have now discovered countless numbers of brown dwarfs that are not associated with any particular star system. They are "floating free", as it were. This makes sense, when we consider a brown dwarf as a "failed star". It could have been the center of its own planetary system, but it just wasn't able to kick-start the nuclear fusion process, and start to burn and glow like a visible star. It may still be, however, the default center of gravity for its very own surrounding mass of substellar material, taking it along for a ride around the galaxy as any normal star would do.

So, perhaps Van Biesbroeck 8b never was a permanent part of the Van Biesbroeck 8 star system. Maybe it was a temporary visitor, or maybe it was recently ejected from the system or swallowed up by the "parent" red dwarf. Perhaps it tried hard to become a satellite of Van Biesbroeck 8 and didn't quite make it, the way that Cruithne tried to become a second moon of Earth in the mid-1980's. One day, perhaps we'll have a better answer.

1995 turned out to be a good year. Not only were astronomers able to confirm 51 Pegasi b as the first true extrasolar planet, we also got the first confirmations of brown dwarfs that continue to be valid today. Gliese 229b was the first brown dwarf detected orbiting a star (in this case, obviously Gliese 229 in the constellation Lepus). Even earlier in this same year, another brown dwarf was confirmed, Teide 1 - in this case an isolated body floating freely about on its own within the Pleiades open star cluster in the constellation Taurus. As many more brown dwarfs were subsequently discovered, they were found both in and outside of other star systems.

A more recent census of brown dwarfs has since concluded that they are quite common, and typically form in the same way that stars do, independently of being part of a star system. In fact, most of the hundreds of brown dwarfs detected so far are out there, on their own, with no star to name as a parent, but possibly with planetary children of their own, according to this 2006 article at the hubblesite.org.

"The universe easily makes brown dwarfs of all masses, from the most massive to the least", says Joan Najita of the National Optical Astronomy Observatory (NOAO) in Tucson, Arizona, after her team used the Hubble telescope and its NICMOS camera to perform a Year 2000 Census of brown dwarfs, with particular focus on the young star cluster IC 348 in the constellation Perseus. Conclusions drawn from this survey suggest that isolated free-floating brown dwarfs form in the same way that stars do, while planets have a very different formation process altogether. The total mass of a brown dwarf may not be the best way to decide if it is a planet or not after all.

While the 2000 Census was able to detect brown dwarfs as small as 15 times the mass of Jupiter - the theoretical lower limit of a brown dwarf, it was only a year or two later that more free-floating sub-stellar objects were found in the star-forming region of the Orion Nebula.... and their masses were as low as 5 to 13 times that of Jupiter. "Are They Planets or What?" asked astronomer Alan Boss of the Carnegie Institution, using that very question as the title of his 2001 news release on the subject. You'll remember Alan Boss from his appearance in the 2007 documentary "Alien Planets", where he discussed his job to review the scientific paper on the discovery of the first exoplanet 51 Pegasi b.

It was Boss's initial computer simulation experiments over a decade earlier that had suggested a number well over 10 Jupiter masses to be the lower limit for any object that forms in the same way as a star - but none of these simulations had taken magnetic fields into account. As Boss performed a new set of calculations including magnetic field effects, it now appears that objects much smaller than 1 Jupiter mass can form using the same method as a star - objects the mass of Saturn. Do these objects qualify to be called planets, or brown dwarfs? Boss suggests the term "sub-brown dwarf". Perhaps the heavens are full of so many more things than we can yet imagine, we need to keep our minds open to invent new terms at any moment....

It seems that brown dwarfs more closely resemble faint stars than planets, and have been "put out to pasture" by many exoplanet hunters. Brown dwarfs, fascinating and controversial as they remain, may not technically count anymore in our exponentially growing lists of extrasolar planets. But for those of us who remember reading about the earliest brown dwarf discoveries, as we thirsted for knowledge of other planets, brown dwarfs are still fascinating, and still an appreciated part of our extrasolar quests. Gliese 229 b is still cool.

For further reading:

hubblesite.org: Hubble Takes Census of Elusive Brown Dwarf Stars, 2000, August 24 This article explains how PLENTIFUL and varied brown dwarfs are, and that mass isn't a good measure for telling the difference between planet/star/brown dwarf.

carnegieinstitution.org: "Are They Planets or What?" 2001, April 3 - detailing Alan Boss's work on brown dwarves and star formation theories, and covering the addition of magnetism to his computer model simulations.

hubblesite.org: Planet or Failed Star? ...One of the Smallest Stellar Companions Ever [Photographed] - 2006, Sept. 7

A history making January 1996 News release from University of California, Berkeley in which Geoff Marcy and Paul Butler, who had confirmed the discovery of the first regular exoplanet 51 Pegasi b, announce the discovery of the next two: 70 Virginis b and 47 Ursae Majoris b. Geoff Marcy also appears in the 45-minute 2007 documentary "Alien Planets", where he discusses the emergence of discoveries of extrasolar planets in the scientific community, and how related careers such as his were vindicated.

John Grayson - Extraterrestrial Life

This book is packed full of known scientific facts concerning astronomy, biochemistry, and conditions on various objects both in our solar system and beyond, up to the then-present day of 1993. Highlights include the discussion of the then-fledgling science of hunting for extra-solar planets, which was largely limited to brown dwarfs at the time. The main focus is on what kind of life might be out there, and where it might practically be found. Overall, a fairly easy and enjoyable read, full of information. Chapter 8 is "Planets of Other Stars" (20 pages), and covers many things including a most in-depth historical look at brown dwarfs.

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Article written by Martin Izsak. Comments on this article are welcome. You may contact the author from this page:

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