Could a rogue planet be the host of a planetary system?

I'll first address Cha 110913-773444 specifically.

Checking the Wikipedia page yields some interesting information:

• Mass: 5-15 Jupiter masses. This means that it is likely a planet - extremely low-mass brown dwarfs are typically in the mid-20s, in terms of Jupiter masses
• Spectral type: L-dwarf. This is consistent with it being a brown dwarf, as many brown dwarfs are of spectral class L or "lower" (i.e. colder). The gist of this is that it doesn't give off a lot of light.
• Luminosity: 0.000096 solar luminosities. This is really, really dim, dimmer than many (possibly most) brown dwarfs. That sounds like a planet.
• Temperature: 1,350 K. This is really low for a brown dwarf, although it may still be one. I'm not sure if that's surface temperature or estimated core temperature. In the latter case, it could be a sign of a massive gas giant.

My completely-non-expert assessment is that it's a planet. But you can disregard that, if you want. Some experts are saying it's a brown dwarf, so you may want to just agree with them. However, some are on the fence:

There are two camps when it comes to defining planets versus brown dwarfs," said Dr. Giovanni Fazio, co-author of the new paper from the Harvard-Smithsonian Center for Astrophysics. "Some go by size and others go by how the object formed. For instance, this new object would be called a planet based on its size, but a brown dwarf based on how it formed. The question then becomes what do we call any little bodies that might be born from this disk - planets or moons?"

Either way, it doesn't seem too conducive for life.

Pre-planet-forming materials have been found around other brown dwarfs, though. As the first article said,

Astronomers have become more confident in recent years that brown dwarfs share another trait in common with stars - planets. The evidence is in the planet-forming disks. Such disks are well-documented around stars, but only recently have they been located in increasing numbers around brown dwarfs. So far, Spitzer has found dozens of disk-sporting brown dwarfs, five of which show the initial stages of the planet-building process. The dust in these five disks is beginning to stick together into what may be the "seeds" of planets.

The second article states,

Apai and his team used Spitzer to collect detailed information on the minerals that make up the dust disks of six young brown dwarfs located 520 light-years away, in the Chamaeleon constellation. The six objects range in mass from about 40 to 70 times that of Jupiter, and they are roughly 1 to 3 million years old.

The astronomers discovered that five of the six disks contain dust particles that have crystallized and are sticking together in what may be the early phases of planet assembling. They found relatively large grains and many small crystals of a mineral called olivine.

The issue is, this thing is small, and its disk may not be massive enough to form planets. If Cha 110913-773444 is a planet, it may not have captured a lot of matter in its disk, because it may have been chucked out of its home system. This means that large bodies may not have formed. If it's a brown dwarf, then it may have accreted more matter. Still, the disk may not be massive enough to form large bodies.

The other issue is the luminosity of the object. Life generally needs solar energy (although tidal forces can produce geothermal heat on a body's satellite) to grow and spread. If this is a planet, it will have a low luminosity, and thus life won't have it easy. If it's a brown dwarf, it will give off more energy, but still not a lot.

In summary, I think it's unlikely life will form. The disk may not be massive enough to form planet-sized (or moon-sized) bodies, and there may not be enough energy for life.

Optimistic Note

I recently asked this question, and it made me realize that it's very possible for this object to accrete matter from a passing star with a debris disk. If someone answers that question, I'll be able to tell you just how much, but I can assume that, given a close enough passing distance and a high enough density, the brown dwarf can accrete a decent amount of matter. It's doubtful as to whether it could capture enough to form a protoplanetary disk (because it's so low-mass), but it's possible

posted about 10 years ago

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