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Gliese 581g: Newsletter Challenge (April 2016)

Posted April 01, 2016 12:00 AM
Pathfinder Tags: challenge questions

This month's Challenge Question: Specs & Techs from IHS Engineering360:

Earth has sent a team of scientists to explore Gliese 581g, a super-Earth exoplanet orbiting a Red Dwarf and located 20 light-years from Earth. Upon approach they marvel that Gliese 581g is almost a perfect sphere considering earlier data. They decide to land in the equatorial region to save fuel. Why?

And the answer is:

The scientists were surprised to learn that Gliese 581g was spherical because of previous data which had told them that it was spinning incredibly rapidly. So rapidly in fact that the centrifugal force at the equator is strong enough to measurably weaken the effect of gravity at its equator, reducing the fuel needed for landing and lift off.

A similar yet much smaller effect occurs on Earth, where the rotation at the equator generates a centrifugal force that reduces effective gravity by one third of one percent.

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#1

Re: Gliese 581g: Newsletter Challenge (April 2016)

04/01/2016 1:23 AM

Maybe they want to fly back to Earth and landing somewhere else would cost more fuel when starting again!

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#2

Re: Gliese 581g: Newsletter Challenge (April 2016)

04/01/2016 2:19 AM

That's where all the tourist destination parks are located....

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#3

Re: Gliese 581g: Newsletter Challenge (April 2016)

04/01/2016 7:06 AM

In general the equatorial region of any planet has the highest rotational and/or orbital angular speed. When arriving from a distant planet, that means that less energy would be spent decellerating in order to land, and likewise less energy would be needed to attain orbital or escape velocity.

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#4
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Re: Gliese 581g: Newsletter Challenge (April 2016)

04/01/2016 11:51 AM
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#5

Re: Gliese 581g: Newsletter Challenge (April 2016)

04/01/2016 10:51 PM

After 20 light years of travel, the earthlings are really fatigued and anxious to get out and take a break from travel so they just head for the widest area to land and stretch their legs.

They all need a quick potty break!

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Re: Gliese 581g: Newsletter Challenge (April 2016)

04/02/2016 9:14 AM

I'm sure that's the answer they're looking for. In practice, the rotational speed of the planet would amount to a miniscule energy savings compared to the energy required for interstellar flight. The orbital motion of the planet would be much larger. (For example, the earth's orbital velocity is about 67000 mph compared with about 1000 mph rotational velocity at the equator.)

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Re: Gliese 581g: Newsletter Challenge (April 2016)

04/02/2016 9:21 AM

Yep. Which is why I replied with rotational and/or orbital speed.

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Re: Gliese 581g: Newsletter Challenge (April 2016)

04/02/2016 4:40 PM

In that case, they might be as interested in longitude as latitude. The "sun" never sets on one side and never rises on the other. I would expect it would be hot on the sunny side, cold on the dark side and windy in between.

If the rotation period is the same as the year (32 days), the equatorial rotation speed would not be of much help.

https://en.wikipedia.org/wiki/Gliese_581_g

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Re: Gliese 581g: Newsletter Challenge (April 2016)

04/04/2016 9:30 AM

My Question:"considering earlier data". What earlier data, since the discovery of this planet was not confirmed by later observations (that could be wrong). We still do not have sufficient data. Tidal lock means there is no turning of day, that the same face is always presented. Warming of the backside (away from the star) is only by circulating winds, which could be very energetic.

Having stated this, I see NO advantage on any significant level to landing, much less landing at the equatorial region, although they is a very slight enhanced orbital velocity on the furthest point from the star. This really only helps with reaching escape velocity from the star.

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#10

Re: Gliese 581g: Newsletter Challenge (April 2016)

04/05/2016 9:58 AM

At the equator region the force of gravity would be some what negative to the rest of the planet because the planets rotation would create a kind of null region thus causing landing and take off easer to achieve.

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Re: Gliese 581g: Newsletter Challenge (April 2016)

04/05/2016 10:15 AM

From the wiki article:

Because of Gliese 581 g's proximity to its parent star, it is predicted to be tidally locked to Gliese 581.

In other words, it hasn't been observed to be tidally locked to its parent star. Keep in mind for a long time they thought the planet Mercury was tidally locked with the Sun and it turned out it wasn't, so "predicted" doesn't really mean anything in the context of this question IMO.

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Re: Gliese 581g: Newsletter Challenge (April 2016)

04/05/2016 12:42 PM

1. centripetal force is higher

2. an orbit other than above the equator requires vectorial forces and inclined orbits

3. star trek is just a picture of money-crazy crackpots

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#13

Re: Gliese 581g: Newsletter Challenge (April 2016)

04/06/2016 8:17 AM

That's where the only landmass is. Leaving the planet from a splash down would use more fuel.

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#14

Re: Gliese 581g: Newsletter Challenge (April 2016)

04/14/2016 10:04 AM

A planet with an Earth-like environment would have to be very close to a Red Dwarf, since they emit much less radiation than stars like the Sun. The proximity to the Red Dwarf would make it likely that it had become tidally locked and, therefore, deformed into a non-spherical shape, due to gravitational forces. However, the question states that Gliese 581g is observed to be almost a perfect sphere ("considering earlier data" - as per Doorman's answer) which implies, in the fictional context of the question, that it is most likely spinning about its own axis to avoid becoming deformed. Otherwise as Usbport's answer.

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Re: Gliese 581g: Newsletter Challenge (April 2016)

04/18/2016 10:16 AM

There is no general requirement for any such planet to be in orbit near a Red Dwarf, unless the star's mass, planetary mass, and orbital period observed dictate this as a solution to the mechanics. Certainly being nearer a red dwarf (if you like them) is better, warmer than being further away, but I prefer blondes (as we have here on Earth). If the planet is in tidal lock, and the orbital period is small, could this have a similar effect as rotational momentum?

I suppose we will never know until we get there. Speaking of getting there, I heard an announcement over the weekend of a consortium preparing a group of small laser-propelled probes to be sent to Alpha Centauri. The probes are to be traveling at a significant fraction of light speed by the end of laser impulse cycling. I bet their little butts will be quite hot for a time thereafter.

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#16

Re: Gliese 581g: Newsletter Challenge (April 2016)

04/19/2016 5:25 AM

I hate to answer this month's question like last months, but, the reasons for landing in the equatorial region to save fuel have already been covered very well.

However, the answer to the question:-

"They decide to land in the equatorial region to save fuel. Why?"

is surely, because it's difficult to find a filling station when you're 20 light years from home.

Incidentally this guy does some really accessible calculations on all sorts of interesting subjects:-

http://mathscinotes.com/2016/04/exoplanet-revolution-period-about-a-dwarf-star/

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Re: Gliese 581g: Newsletter Challenge (April 2016)

04/19/2016 9:32 AM

That was a particularly well phrased explanation, and was relatively easy to follow (for a change). Thank you for sharing.Cheers!

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