APOD: A View from Next Door (2012 Oct 18)

[APOD Robot]

A View from Next Door

Explanation: Located just next door, Alpha Centauri is the closest star system to the Sun. A view from our interstellar neighbor a mere 4.3 light-years away is shown in this illustration. The Sun is at the upper right, a bright star against the background of the Milky Way. The cresent in the foreground is an artist's rendering of a planet now reported orbiting Alpha Centauri B, making it the closest known exoplanet. Discovered by astronomer Xavier Dumusque et al. using the planet hunting HARPS instrument to measure minute shifts in the star's spectrum for more than four years, the planet has approximately the same mass as Earth. But it orbits once every 3.2 days, about 0.04 times the Earth-Sun distance from its parent star. That puts it well outside the habitable zone, much too close to Alpha Cen B, a star only a little cooler than the Sun. Still, estimates indicate that planetary orbits would be stable within the habitable zone of Alpha Cen B, at about half the Earth-Sun distance ...

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[bystander]

http://asterisk.apod.com/viewtopic.php?t=29788

[hstarbuck]

Now this is news that I am excited to hear! Think how many times this star system is mentioned because it is the nearest to Earth. Now at least 1 planet can be mentioned with it, and one that is near the Earth in mass at that! What other "famous stars" have known planets?

[Jim Leff]

This is not huge astronomical news, given that we've already found some 842 extrasolar planets. But this may represent a turning point for humanity. If a planet is found within that habitable zone, human imagination will turn toward Alpha Centauri B. It's starting to look like the next destination.

Even at the dizzying speed of our Voyager spacecrafts, it's a 40,000 year journey. But now there's fresh impetus to develop some of the interesting proposed means for human-viable interstellar travel. http://en.wikipedia.org/wiki/Interstellar_travel

[starsurfer]

Whilst it may not be new news, the feeling is profound and thought provoking, think of all the planets we haven't found!
Also there is a small spelling mistake, crescent is spelt as cresent.

[Snow Leopard]

The exoplanet findings as mentioned in discussion for Alpha Centauri B are at best hypothetical. Its an 'i dont know' situation :-/ deriving conclusions from very indirect observation. Examination of the star's spectrum may not necessarily yield info about associated exoplanets; the data may just as well suggest that the star has a giant sunspot which revolves around surface of star once every 3 days. Even so, the artists rendering is well appointed.

It is thought that Alpha Centauri A has an Earth-like terrestrial world at placement 4 - hence, the name of the planet is designated Alpha Centauri Majorum IIII. Distance of planet to parent star is expected to be approximately 1.47 AU. The planet is thought to have two moons - one large moon with a sparse atmosphere and one small moon which orbits in the distance. The two moons are tidally bound to the planet, like the Earth-Moon system, so that the same side of each faces the planet. Two additional planets must exist beyond Alpha Centauri Majorum IIII. An asteroid field probably exists at about 6 AU. Beyond the asteroid field is the realm of Alpha Centauri B.

[MadMan]

It is thought that Alpha Centauri A has an Earth-like terrestrial world at placement 4 - hence, the name of the planet is designated Alpha Centauri Majorum IIII. Distance of planet to parent star is expected to be approximately 1.47 AU. The planet is thought to have two moons - one large moon with a sparse atmosphere and one small moon which orbits in the distance. The two moons are tidally bound to the planet, like the Earth-Moon system, so that the same side of each faces the planet. Two additional planets must exist beyond Alpha Centauri Majorum IIII. An asteroid field probably exists at about 6 AU. Beyond the asteroid field is the realm of Alpha Centauri B.

What is your source for this information?

[Devil Particle]

Pardon the crude drawing but does the calculation of the mass of the planet take into consideration the inclination of its orbit?

[pipejazz]

Sagan would have thought this so cool...

[neufer]

This is not huge astronomical news, given that we've already found some 842 extrasolar planets. But this may represent a turning point for humanity. If a planet is found within that habitable zone, human imagination will turn toward Alpha Centauri B. It's starting to look like the next destination.

Even at the dizzying speed of our Voyager spacecrafts, it's a 40,000 year journey. But now there's fresh impetus to develop some of the interesting proposed means for human-viable interstellar travel. http://en.wikipedia.org/wiki/Interstellar_travel

[b][color=#0000FF]Distances of the nearest stars from 20,000 years ago until 80,000 years in the future. Proxima Centauri is in yellow[/color][/b]

---

One wouldn't want to send humans for all sorts of reasons.

Nor should one take longer than about 27,400 years to get there on a robotic mission because that would be the time of it's closest approach at a distance of ~ 3 light years.

But it would probably be silly to consider any voyage that would take more than 1,000 years for political & inspirational reasons:

• "We choose to go to Alpha Centauri in this millennium and do the other things, not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win, and the others, too."

Current technology:

• After multiple gravity assists the 5,600 kg Cassini spacecraft finally left the Earth/Moon system at just ~3 km/s shy of Solar System escape velocity. Presumably a Saturn V could place a 47,000 kg spacecraft into a similar (near solar system escape velocity) trajectory.
  
  Such a 47,000 kg spacecraft could (given an effect Xenon ion exhaust velocity (Ve) of 29 km/s) launch a ~800 kg interstellar probe that escapes the solar system at a velocity of 120 to 150 km/s = a relative velocity vis-a-vis α Centauri of 140 to 170 km/s.
  
  Such a probe could reach α Centauri (or Barnard's star) in from 7700 to 9400 years.

[Keyman]

Pardon the crude drawing but does the calculation of the mass of the planet take into consideration the inclination of its orbit?

From ESO1241 — Science Release

[3] Using the radial velocity method, astronomers can only estimate a minimum mass for a planet as the mass estimate also depends on the tilt of the orbital plane relative to the line of sight, which is unknown. But, from a statistical point of view, this minimum mass is often close to the real mass of the planet.

Well played, Devil. Well played...

[Jim Leff]

One wouldn't want to send humans for all sorts of reasons

Such as?

But it would probably be silly to consider any voyage that would take more than 1,000 years

National Geographic quotes UC Santa Cruz astronomer Greg Laughlin as saying:

Though the new world is being branded the planet next door, it's still four light-years away. It would take our best current robotic spacecraft about 40,000 years to travel that distance, estimated Greg Laughlin, an astrophysicist at the University of California, Santa Cruz, who was not part of the Swiss team but who participated in the press conference.

That could change, however, "if there's a public groundswell to get to Alpha Centauri," Laughlin said—for example, if other planets are found orbiting Alpha Centauri B, especially in the system's habitable zone, where temperatures would be friendly to life.

In that case, he said, "it's possible that new technology could be developed to get a spacecraft there from Earth in a human's life span."

http://news.nationalgeographic.com/news ... space-udry

That's also, btw, where I got the 40,000 year figure.

[Grizzly]

Nipticking, I know, but if the planet's orbit is that close in to the star, shouldn't the star in the image be considerably larger?

[emc]

Orin, we’re gonna need a faster wheelbarrow!

[Anthony Barreiro]

Oh my. My understanding is that it is highly likely that an orbiting planet accounts for the observed doppler shift in Alpha Centauri B's spectrum, but the data are right at the limit of detection, and there are several other possible explanations. By all means let's try to confirm this hypothesis, but it might be a little premature to start loading up the starship just yet. The spirit of Davy Crockett lives on: when I can detect the infrared spectrum from my neighbor's fusion reactor, it's time to pull up stakes and homestead the next solar system.

[neufer]

Nipticking, I know, but if the planet's orbit is that close in to the star, shouldn't the star in the image be considerably larger?

Judging from the separation of Alpha Cygni from Gamma Cygni in the background
I'd estimate that the size of Alpha Centauri B was about 12º in diameter
(~24 times the angular size of the Sun from the Earth)
which seems about right for a distance of 0.04 AU.

[neufer]

One wouldn't want to send humans for all sorts of reasons

• Such as?

• ________ Scientific American JUNE 1960
  
  "Putting a man in space is a stunt: the man can do no more
  than an instrument, in fact can do less." So said Vannevar Bush,
  chairman of the Board of Governors of the Massachusetts Institute
  of Technology, in a statement to the House Committee on Science
  and Astronautics. "There are far more serious things to do than to
  indulge in stunts. As yet the American people do not understand the
  distinctions, and we in this country are prone to rush, for a time, at
  any new thing. I do not discard completely the value of demonstrating
  to the world our skills. Nor do I undervalue the effect on morale of
  the spectacular. But the present hullabaloo on the propaganda
  aspects of the program leaves me entirely cool."

[Boomer12k]

I did a project in a College Science class on the possible existence of planets in the galaxy...no one of course took it seriously, or if they did, they kept their mouth shut...this was 1973 or 1974...

Now there appears to be planets everywhere we look and not always what, nor where, we expect...

Too bad I am not one to say..."I told you so."....oh...that's right....I AM!!!!!

:---[===] *

[richard schumacher]

Well, harrumph. The name of Earth's sun is "Sol", not "Sun". ESO and APOD ought to hold the line on this.

[chanio]

I imagine living in a world with two suns. The bigger being colder than the smaller.
At Winter, it would be like living in the South Pole.
And in Summer like living at the Sahara desert.
But watching always two suns and two moons.

The planet having mostly the same earthquakes and volcanos than ours.
But the (presumably living there) people's personality should be like the Vulcans of the Startreck series. Strong, cold and rational. Because of their landscape and weather.
If that is the case, then they would probably come to visit us before we start building such a powerful spaceship that could take us there...

[neufer]

Note that those folks living on the dark side of Alpha Centauri Bb
would have days 3.2 earth days long as Alpha Centauri A
(with 152% the luminosity of the Sun) rises & sets 23 AU away.

[Hukadarn]

I remember that Javiera Guedes (Department of Astronomy and Astrophysics, University of California) in 2008 published a paper in the Astrophysical Journal with the results of simulations ( using the softwares Mercury and Systemic) which indicated that Alpha Centauri B could offer conditions to the formation of a planet with a mass similar to Earth in its orbit (and others some with!).

Below the final distribution of orbits in different simulation times, not encouraging?

Click to view full size image

The paper and additional details of the simulations can be read here:

- http://arxiv.org/abs/0802.3482
- https://webhome.phys.ethz.ch/~jguedes/alphacen.html

[ ]´s

[Sam]

One wouldn't want to send humans for all sorts of reasons

Such as?

Du aber, Mensch, wie lang lebst denn du?
Nicht hundert Jahre darfst du dich ergötzen
an all dem morschen Tande dieser Erde!

Click to play embedded YouTube video.

[You, Man, how long do you live?
Not even a hundred years may you enjoy
all the mouldering trinkets of this Earth!]

--
Sam

[neufer]

I remember that Javiera Guedes (Department of Astronomy and Astrophysics, University of California) in 2008 published a paper in the Astrophysical Journal with the results of simulations ( using the softwares Mercury and Systemic) which indicated that Alpha Centauri B could offer conditions to the formation of a planet with a mass similar to Earth in its orbit (and others some with!).

• Hmmmm......Javiera Guedes

That wouldn't be an "alien" name would it

[bystander]

I remember that Javiera Guedes (Department of Astronomy and Astrophysics, University of California) in 2008 published a paper in the Astrophysical Journal with the results of simulations ( using the softwares Mercury and Systemic) which indicated that Alpha Centauri B could offer conditions to the formation of a planet with a mass similar to Earth in its orbit (and others some with!).

Below the final distribution of orbits in different simulation times, not encouraging?

https://lh5.googleusercontent.com/-1y6H ... oard02.jpg

The paper and additional details of the simulations can be read here:

- http://arxiv.org/abs/0802.3482
- https://webhome.phys.ethz.ch/~jguedes/alphacen.html

[ ]´s

Are There Planets Around Alpha Centauri?
Universe Today | Fraser Cain | 2008 Mar 10

Nearby star should harbor detectable, Earth-like planets
University of California, Santa Cruz | 2008 Mar 06

Formation and Detectability of Terrestrial Planets around α Centauri B - Javiera M. Guedes et al

• Astrophysical Journal 679(2) 1582 (2008 Jun 01) DOI: 10.1086/587799
  arXiv.org > astro-ph > arXiv:0802.3482 > 25 Feb 2008 (v1), 17 Mar 2008 (v3)