Habitabilty zone for a white dwarf

[phavoc]

I was doing some reading on stars and have a question. It is theoretically possible to have a planet orbiting a white dwarf that would fall within the habitabilty range correct? I'm not talking a earth-like world, because it would not be able to form, but you could have a really crappy world, but one that is livable, err, more like survivable, right?

I'm thinking more of say a planet that was captured by the star after it became a white dwarf, which would mean I wouldn't have to justify how it wasn't a cinder before the star turned into a white dwarf.

Any ideas if this is possible?

 

[barnest2]

You could have a really crappy rogue planet being captured by a white dwarf. It would be truly crappy though. It probably wouldn't have an atmosphere.

 

[BP]

Sure - theoretically possible - why not?

We know a habital planet can exist. We know dwarf stars appear to exist. One can theorize the two together, however improbable.

The actual formation of the dwarf could, theoretically mind, somehow form the conditions necessary - stating it could not is, at best, just being overconfident. Theories are just that - theories. Especially when it comes to astronomy and stellar sciences - they change relatively frequently as new information and revelations occur.

A planet could be captured or even formed (or transformed) during the creation of the star with just the right scenario to form an atmosphere (out-gasing from extreme seismic activity). The planet could also have been far enough out that perturbations from the passby of interstellar object(s) could have resulted in orbit changing to bring it into the habitable zone - also causing the thawing/and or tectonics ultimately resulting in an atmosphere, maybe even breathable.

 

[zero]

When Sol goes White Dwarf, will Mars be swallowed up before or will it be on the outer edge? You could have a planet at that position (approx 1.5 AU from the Star).

Of course, as said, it will be a planet like Mars, so it'll need to been colonised by a race and made ok to live on artificially, by some whose planet was swallowed at an earlier date and they chose that world as their new homeworld?

Just a few ideas.

 

[Rick]

When Sol goes White Dwarf, will Mars be swallowed up before or will it be on the outer edge? You could have a planet at that position (approx 1.5 AU from the Star).

Of course, as said, it will be a planet like Mars, so it'll need to been colonised by a race and made ok to live on artificially, by some whose planet was swallowed at an earlier date and they chose that world as their new homeworld?

Just a few ideas.

As far as I'm aware, Venus and Mercury would be swallowed up into the Red Giant stage, Earth would possibly be 50/50, but if it survived would be a barren ball of rock; Mars and the outer planets would be structurally ok, but once the star collapsed they'd be engulfed in a planetary nebula, possible extreme levels of radiation hitting the surfaces as well for a few hundred/thousand years (not sure how long the collapse and nebula would last for). Any civilisation that wants to live through all that would have to be deep underground and self-sufficient, I would guess - even then I wouldn't like to give odds on their survival.

 

[BP]

Mars' orbit would probably be way too far out... at least for the OP's 'habital zone' for white dwarfs. However, if the planet ends up real close, but outside the Roche limit, they may make a better 'Earth-like' planet than Earth - with respect to time!

Hmmm... recall something about exo-planets around WDs from earlier this year...<quick google>... try this: http://arxiv.org/pdf/1103.2791v2

EDIT: A more approachable link: http://www.space.com/11375-alien-planets-dying-stars-white-dwarfs.html

I'm a huge fan of science, but our knowledge of extrasolar planets is just, just really beginning as we peer beyond our solar system with more recent space-based instruments - and so far many of the commonly accepted preconceptions about possibilities and probability have proven to be incomplete or even inaccurate. The next few years hold lots of exciting promise for expanding and 'correcting' our view of the universe at the planetary scale.

 

[GypsyComet]

The liquid water zone (aka the "Habitable Zone") around an aged and stable white dwarf is going to be dancing with the star's Roche limit. As already noted by others, a planetary body in such a position would have to be a recent capture or a recently assembled "dustball", as nothing solid that was in that orbit during the star's Main Sequence period would have survived to the dwarf stage, assuming that orbit was viable at all during the earlier stages.

Worlds in the outer system might have had brief (cosmologically speaking) Springs as the star expanded, but would, by the Dwarf stage, be either barren rockballs, ragged looking old Giants, or the rare super-terrene or big pan-thallasic with a likely exotic atmosphere. The worlds in the best shape would be the distant halo dwellers, and they were never very warm at any stage.

You want to get bogglingly bizarre, set a small captured exo-giant with a single moon in close orbit around an ancient white dwarf, no two orbital planes or rotational axes even close to related. Between the waste heat of the giant and the wan light of the star, the moon might just be capable of supporting liquid water. Of course, the aged and doomed life that has managed to take hold is strangely more tolerant of solar energy than its environment calls for, since the star and the giant are in a slow vampire/flare relationship, and things get very bright every few thousand years...

 

[BP]

Don't have to be 'recent'... WDs live a long time and formed as early as a Gy after the Big Bang

Till more recent times (and space based instruments like WMAP!), WD temps were used a one means to estimate the 'Age of the Universe'.

An outer planet has plenty of time to migrate into a stable orbit close in to a WD's habitable zone, or even for planets to coalesce from a dust cloud after its creation. The oldest WDs in our Milky Way galaxy could easily have supported Earth's paltry 4.5 billion or so years...

 

[GypsyComet]

"Recent" was a stand-in for "since becoming a white dwarf".

 

[BP]

Ah - makes sense, my bad. It was a good post, the 'recent' just threw me, and wanted to make sure it was clear the planet could easily be old enough to develop life.

 

[Rikki Tikki Traveller]

It is extremely, extremely, EXTREMELY unlikely that a planet could exist in the habitable zone of a white dwarf.

The planet would have had to migrate there after the star went nova and became a white dwarf (unlikely but certainly possible).

However, the biggest issue is the location of the habitable zone. For a "typical" white dwarf, it has a Luminosity of about 0.0005 Sol (yes, 0.5% of Sol), so the habitable zone is about 0.015-0.03 AU from the star.

At that distance, the tidal forces from a typical white dwarf are going to be HUGE, much bigger than the forces from a Red Dwarf star at the same distance. Also, since the habitable zone is so small, it is very unlikely that a planet will settle into a stable orbit at that distance (and only within that distance).

The planet would be tidally locked.

Yes, it could happen, but a lot of things have to line up just right to make to happen. Probably much less than once per sector and more likely only a couple of times (at most) in the entire galaxy. That's 1 in 100,000,000,000 chance (ish).

But yes, it is possible.

 

[phavoc]

That actually works out great. I was wanting a planet with the nickname applied as "Hell", or "The Rock". I wanted it to be a crappy place, with a crappy atmosphere. Tidal locked works great because one side of the planet will be roasting hellhole, the other side a frozen hellhole, and people "living" in between the two zones.

Thanks for the tips!

 

[zero]

So basically a planet like Mercury with some water then? 8)

 

[phavoc]

Not as harsh as mercury. I stil want an atmosphere, and it to be "inhabitable" without special enviro suits. Atmo would be tainted, landscape rather barren, and harsh conditions. I was inspired for something like this by playing the game Borderlands.

With conditions like that, it's ripe for a few adventures.

 

[Rikki Tikki Traveller]

It might not be all that hot on the day-side either. Remember, the density of a White Dwarf is much higher than normal stars, so planets will be tidally locked much farther out, relative to the habitable zone, than around normal stars.

It is quite possible that the day-side temperature never gets above freezing...