
Scientists to unveil new Earth-like planet - vinnyglennon
http://m.phys.org/news/2016-08-scientists-unveil-earth-like-planet.html
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tootie
Project Longshot estimates 100 years to reach Alpha Centauri B. And that's
assuming we launch tomorrow. Add 4 years to receive the telemmetry.

[https://en.wikipedia.org/wiki/Project_Longshot](https://en.wikipedia.org/wiki/Project_Longshot)

~~~
Retric
That's ~1000 times the velocity of our fastest probe so far when you exclude
gravity assist. Stopping at the other end doubles travel time.

~~~
lucb1e
> Stopping at the other end doubles travel time.

Wow, I knew the physics but never realized the implication: where on earth
hitting the brakes is easy and costs next to zero energy, in space breaking
takes just as much energy as accelerating.

~~~
soneil
I know it's a game, but Kerbal Space Program really helped hammer home a lot
of the things I guess I understood in the abstract. Delta-V is Delta-V. Every
change in velocity (ignoring external influences) is cost out of the same
budget. Braking is just accelerating in the opposite direction.

~~~
fbonetti
Before I played KSP I had a lot of hilarious misconceptions about the physics
of rocketry and space travel.

On my first attempt to get into orbit, I loaded up my rocket with as many
engines and boosters as I could strap on and fired the rocket straight up. The
rocket breached the atmosphere but to my surprise the rocket came straight
back down. I literally thought that launching rockets into orbit meant
shooting them really high until they were "in space" haha. I then quickly
learned that being in orbit means having a horizontal momentum that is
balanced with the gravitational pull of a given body. This balance produces a
curved elliptical trajectory.

~~~
Noseshine
And you have to _decelerate_ to catch up to the station in orbit. If you
accelerate you will fall back.

That's because if you fire your rockets to accelerate you end up in a higher
orbit, i.e. your circle is much bigger, and vice versa, to overtake/catch up
you want to fall to a lower orbit. That's also not intuitive to someone with
"earth-experience".

~~~
mrfusion
Yet objects in higher orbits like the moon are going way slower around the
earth than low earth orbits.

What's the deal with that?

~~~
db48x
Higher circular orbits are indeed slower than lower ones. The shuttle goes
around the earth in 90 minutes, the moon takes 28 days. Geosynchronous orbit,
where one orbit takes one day, is in between.

What's confusing about transfers is that elliptical orbits are orbits where
your velocity varies based on where you are in the orbit. Your speed is
highest at perigee and lowest at apogee. In fact, your speed at perigee will
be higher than the speed of an object in a circular orbit at that altitude.
The reverse is true at apogee; your speed will be slower than an object in a
circular orbit at the same altitude.

So if you and your docking target are both in circular orbits, and you
increase your speed in order to catch up, then you will simultaneously be
raising the other side of your orbit, half a turn away. The difference at your
current location will be minute, but will grow every continuously over that
half a turn. If you're docking in the next few seconds it won't be a problem
(the docking mechanism will handle a small offset, and it equalizes your
speeds provided the difference isn't too much). If you're still several
minutes away, however, you might find that the extra radial velocity means
that you fly over the top of your target.

If you miss and continue to follow your new orbit you will indeed find that
your overall time to orbit is now higher than your target's. It may be many
orbits before you again have a close approach with your target, although if
the difference in speeds is small then it may appear from your perspective
that you are in fact orbiting your target.

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theodorejb
It took 9.5 years for New Horizons to reach Pluto (just 32 astronomical units
distant). At that rate, it would take a probe more than 80,000 years to cross
the 271,000 AUs separating Earth from this exoplanet.

~~~
mabbo
That presumes a constant velocity. Any extra-solar ship would certainly need a
different acceleration profile. Ion engines come to mind: low acceleration,
but constant for a very long time. If you're going a far distance, they're
ideal.

~~~
dalke
While you have a valid point, here's what it works out for ion engines.

Assume you want 1,000 years to Alpha Centauri and your ship boosts the entire
way. (It'll take a few pictures as it flies through the system.)

    
    
      s = 1/2 a t^2
      a = 4.22 light years * 2 / ((1000 years)*(1000 years)) = 8 E-5 m/s/s
    

Sounds great, right? But the final speed is:

    
    
      v = a * t = 4.22 light years * 2 / (1000 years) = 2.5E6 m/s = 0.8 c (!)
    

Let's say your engine has a ISP of 8000 s, which is about 10x better than
anything we have.

Then from the rocket equation you'll need a dry weight (payload, engines,
etc.) to propellant ratio of

    
    
      e^(2500000 / (9.8 * 8000) = 70,579,094,313,732 = 71 quadrillion
      eg, 1 gram of spacecraft requires 70 kilotons of propellant
    

But wait, there's more! It takes power to push 70 kilotons of propellant
backwards at 80,000 m/s.

    
    
      E = 1/2 * m * (v^2) = 2E20 Joule
      Since E = m c^2
       => total annihilation of over a ton of antimatter
    

Almost certainly more as that assumes 100% efficiency. And of course that
extra ton isn't propellant, so it hits you in the rocket equation.

Note: I am not a rocket scientist and likely made mistakes. Even if I'm off by
a few zeros, it's enough to show that an ion engine isn't going to get
something to Alpha Centari within a few centuries.

~~~
dalke
Oops! There's a couple of missing zeros. The 2.5E6 m/s = 0.8 c should be 0.8%
c. That mistake doesn't continue to the rest of the calculation.

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digdigdag
I don't think there are electronic or software components today that can
withstand interstellar space travel for thousands of years, even at the
distance of proxima centauri.

Distance is irrelevant when it comes to space travel. Unless an object is
within the vicinity of the Oort cloud, we stand very little chance of actually
leaving this solar system in a controlled fashion.

~~~
madaxe_again
Well, the key is to not take thousands of years about it. Honestly, I doubt we
will ever have thousand year missions, unless our lifespans commensurately
grow, as humans don't have a great track record when it comes to long term
projects.

There are ways, but they are expensive and not without risk. Nuclear pulse
propulsion (orion) can yield vast acceleration, and fusion rockets, while
unproven, are feasible. You then have less exotic options such as laser driven
light-sails and nuclear powered ion drives.

If we were prepared to throw half a trillion bucks at the problem we could see
a flyby in our lifetimes - but without a damn good reason, it won't happen.

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jagger27
I wonder if the James Webb Space Telescope will be able to image it since it's
so close.

~~~
danpalmer
Can anyone "do the maths" on this. I don't feel well enough equipped, but I'd
love to know the feasibility of this, or what we would be able to image if
anything.

~~~
cnvogel
A planet the size of the earth at the distance of proxima centauri is about
6.582⋅10^-5 arcseconds wide (a 20'000th of an arcsecond)

angle(in degrees) = size / distance / pi ⋅ 180°, take times 3600 for arc
seconds

[https://www.wolframalpha.com/input/?i=(diameter+of+the+earth...](https://www.wolframalpha.com/input/?i=\(diameter+of+the+earth\)%2F\(distance+to+proxima+centauri\)+%2F+pi+*+180+*+3600)

I didn't find a easy round number for James Webb, but Hubble's angular
resolution is 1/10th of an arcsecond, at least a factor 2000 too low to even
resolve the planet's disk as one pixel.

[https://www.spacetelescope.org/about/faq/](https://www.spacetelescope.org/about/faq/)

~~~
dalke
[http://jwst.nasa.gov/faq_solarsystem.html#angularresolution](http://jwst.nasa.gov/faq_solarsystem.html#angularresolution)
says:

> The specification is that the telescope is diffraction limited at 2 μm,
> which means a Strehl ratio of 0.8 and a wavefront error of 150 nm rms. With
> a 6.5 m telescope, 1.22 λ/D = 0.077 arcsec at 2 μm. The smallest pixels
> (NIRCam 0.6-2.5 μm) are just 0.034 arcsec. But a lot of the wavefront error
> is due to imperfect alignment of the parts, and it's possible to do better
> for a small part of the field of view.

A telescope can still detect something smaller than its resolution. We can see
stars with our eyes, after all. Even astronauts in space, where there is no
atmosphere to move the light around. Here are some of the best attempts at
direct imaging with a telescope: [http://www.planetary.org/explore/space-
topics/exoplanets/dir...](http://www.planetary.org/explore/space-
topics/exoplanets/direct-imaging.html)

The problem is the planet is dim and close to a bright star. If this planet is
1 AU out, then there's a 0.77 arcsec between it and the the star, which would
make it easier to distinguish the two.

~~~
dharma1
Quantum telescopes should get us beyond the diffraction limit

[http://arxiv.org/pdf/1508.04275v4.pdf](http://arxiv.org/pdf/1508.04275v4.pdf)

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sevenless
Moving matter around takes far too long for star travel. We need to figure out
how to assemble machines from long distances using light. (Something like
[https://en.wikipedia.org/wiki/Optical_tweezers](https://en.wikipedia.org/wiki/Optical_tweezers))

~~~
Teever
Why not just launch a seed factory and send the instructions to build via
light?

That seems a hell of a lot more practical and cost effective

~~~
kyzyl
Also more possible haha. It's all fun and games until you predicate the
success of your project on trying to collimate a laser beam from here to alpha
centauri, so that it can manually assemble a (dielectric!) robot one
piconewton at a time.

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dTal
This is extremely exciting! The million dollar question is of course "how
Earth-like?". If the answer is "very" we might actually have found a viable
place for an off-world colony!

Getting a probe there in a reasonable time is entirely feasible if can figure
out how to keep the darned thing accelerating without stupendous fuel
requirements. I'm confident we'll figure that out sooner or later.

~~~
denim_chicken
Keep dreaming. If we cannot even understand or live in accordance with the
life support systems of what is literally the most habitable and human-
friendly planet in the Universe then there's no way in hell that we will be
able to successfully colonize a lifeless planet.

Stop thinking about outer space when we are in the middle of an anthropogenic
mass extinction here on planet Earth.

~~~
gwright
I'm going to assume this is a serious comment and that you are attributing
global warming as the cause of the feared extinction.

In that case I think you should dial it back a bit. Humans are pretty
adaptable. Even assuming the changes in temperature and sea-level are on the
high end of predictions, we will adapt. People will move, infrastructure will
be built, and so on. Mass extinction certainly isn't going to happen from
global warming as we understand it today.

You might argue there there will be mass casualties, but that is also
uncertain, difficult to quantify, and is quite a different thing than 'mass
extinctions'. Of course, mass casualties due to weather has and is already a
problem -- it isn't something that is uniquely associated with global warming.

~~~
chriswarbo
> Mass extinction certainly isn't going to happen from global warming as we
> understand it today.

I assume the parent is referring to the
[https://en.wikipedia.org/wiki/Holocene_extinction](https://en.wikipedia.org/wiki/Holocene_extinction)
which is certainly happening, and has been for thousands of years.

Climate change is a rather recent contributor, albeit a very serious one of
which we've only glimpsed the beginning.

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grondilu
I vaguely recall a quote saying that if an Earth-like planet was ever found
around Proxima Centaury, an international project to build an interstellar
probe would begin immediately.

Well, we'll see.

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rcarmo
Can't wait for the "small furry creatures from Alpha Centauri" memes.

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npace12
It's probably Trisolaris

