Wednesday, March 17, 2010
Cower in Terror....Only not right now.
Gliese 710 hurtles towards an unsuspecting Sun (which is too dim to be seen in this Celestia image*)Passed on by commenter JupiterIsBig. Be afraid, be .. somewhat afraid.. for the star Gliese 710 is hurtling our way and will cause a lethal hail of comets in .. well.. in 1.5 Million years. I'm not starting building the impact shelters yet. By the time it comes close we will probably be able to move stars around at will anyway (or be long extinct, one or 'touther).
What does this demon star of doom look like. Well, if you could see it from Australia tonight, (which you can't as it is below the horizon), you would need a small telescope to see the inauspicious magnitude 9.2 star just below eta serpens. It may look harmless now, safely 63 light years away, but whoompph! By a mere 1.5 million years it will be within 1.1 light years and will wreak havoc with our Oort cloud and Kuiper Belt, causing an umm, maybe a 5% increase in comet impacts?
Yes, I'm shaking in my boots.
The abstract of the paper is here, and the full paper here.
*sadly, tragically, you can set the date to 1.5 million years ahead in Celestia, but it doesn't move the stars according to their radial velocity. I'll try and come up with a fix.
Labels: miscelaneous, peer-reviewed research, weirdness
Thursday, December 17, 2009
An Earth-like world, around a Sun-like star, but ....
Next time you are up in the morning looking at Saturn and Mars, let your eye wander over and down to Spica, the brightest star in the constellation Virgo. About halfway between that and the brightish star Gamma Hydri, is a dim, unprepossessing star; 61 Virginis (helpfully highlighted in the diagram opposite).A mere 28 lightyears away, 61 Virginis is a Sun-like star that harbours at least three planets, discovered in a joint venture between the Keck Observatory and the Anglo-Australian Telescope (yes, Aussies had a hand in this) using radial velocity measurements . Measurement of minute Doppler shifts in the stars spectrum lead to the conclusion that the system has two Neptune like worlds, and one Super-Earth of 5 Earth masses, 61 Virb. The other reported 5x Earth Mass planet Gliese 581c, orbits a Red Dwarf star.
Although the star is Sun-like, and the planet is Earth-like (if a 5x Earth mass is sufficiently "Earth" like), the orbit is not. 61 Virb screams around its sun in 4.2 days, in an orbit well inside that of Mercury (not as close as WASP 18b though). The two Neptune mass planets 61 VirC and 61 VirD are also inside the orbits of Mercury and Venus, respectively, on elongated orbits. So this is a very "unsolar" solar system, unlike GJ 758b, which is a Jupiter-like planet in a solar system-like orbit around a Sun-like star.
The orbits of 61-Virginis b, c and d. B and c orbit closer than Mercury does to our sun (this and above image generated with Celestia).You can read the original press release here. You can read the paper that will be published soon in The Astrophysical Journal here.
If you want to add the 61 Virginis system to Celestia, cut and paste the parameters below to a file and save it as 61Virb.ssc in the extras folder of Celestia.
=====================8<=cut===================================
"b" "HD 115617"
# 61Virb, vying for lowest mass exoplanet yet, with sunlike star
{
Texture "venuslike.*"
NightTexture "venuslike.*"
#Color [0 0.36 1]
#Albedo 0.05
Mass 5.1 # M.sin(i) = 5.1 Earths
Radius 12600
InfoURL "http://en.wikipedia.org/wiki/61_Virginis_b"
EllipticalOrbit {
Period 0.0115
SemiMajorAxis 0.05021
Eccentricity 0.12
Inclination 86
ArgOfPericenter 105
MeanAnomaly 166
}
Obliquity 82 # guess, to match inclination
#EquatorAscendingNode 96 # guess, to match ascending node
# likely to be in captured synchronous rotation
}
AltSurface "limit of knowledge" "HD 115617/b"
{
Texture "extrasolar-lok.*"
}
"c" "HD 115617"
# 61Virc Neoptune like with sunlike star
{
Texture "exo-class2.*"
Color [0.98 0.97 1]
Albedo 0.75
Mass 18.2 # M.sin(i) = 18.2 Earths
Radius 49528
InfoURL "http://en.wikipedia.org/wiki/61_Virginis_b"
EllipticalOrbit {
Period 0.1041
SemiMajorAxis 0.2175
Eccentricity 0.14
Inclination 86
ArgOfPericenter 341
MeanAnomaly 177
}
Obliquity 82 # guess, to match inclination
#EquatorAscendingNode 96 # guess, to match ascending node
# likely to be in captured synchronous rotation
}
AltSurface "limit of knowledge" "HD 115617/c"
{
Texture "extrasolar-lok.*"
}
"d" "HD 115617"
# 61Vird another Neptuneoid, with sunlike star
{
Texture "exo-class4.*"
NightTexture "exo-class4night.*"
Color [0 0.36 1]
Albedo 0.05
Mass 22.9 # M.sin(i) = 22.9 Earths
Radius 51118
InfoURL "http://en.wikipedia.org/wiki/61_Virginis_b"
EllipticalOrbit {
Period 0.3368
SemiMajorAxis 0.476
Eccentricity 0.35
Inclination 86
ArgOfPericenter 314
MeanAnomaly 56
}
=====================8<=cut===================================
Labels: exoplanet, extrasolar planet, Observational Astronomy, peer-reviewed research
Saturday, September 05, 2009
From eccentric to well behaved - Are there invisible companions to known exoplanets
The 373 exoplanets we have discovered so far are a strange bunch. Mostly way larger than Jupiter, around 40% scream around their stars closer than Mercury orbits our sun. This is probably mostly due to detection bias, as we find most of the exoplanets by detecting tiny (really, really tiny) wobbles in their parent stars orbits. Detecting a planet of Jupiters size in Jupiters orbit would take many years of close scrutiny. As well as the sizes and locations, many of the exoplanets have strange (at least from our perspective) orbits. All planets have eliptical orbits. But while in our solar system most of the plants have orbits that are quite close to circular (see image top left) many extrasolar systems have orbits that are far more eccentric, almost cometary (see the system for Mu Ara above right)
Now, the weird orbits may be a result of how the super Jupiyters get close to their stars. We believe that latge, Jupiter -like planets form far from their stars, and then migrate in by interaction with other planets (Hot Jupiters have probably ejected any Earth mass planets from the stars equivalent of the inner solars system).This series of cosmic billiards may leave the hot Jupiters with very elongated, comet like orbits.
However, as for most of the planets, we are inferring the orbits from tiny wobbles, there may be some error in deriving these orbits, especially for orbits of single planets that are only mildly eccentric (see HIP 25110 above). A recent paper suggests that the gravitational tugs of unseen companions to known exoplanets could make their orbits appear more elliptical than they really are. The authors used a simulation where they generated a range of exoplanetary systems containing roughly equal numbers of single and double worlds. They then looked at the distribution of eccentricities in this simulated sky, and gfound that it matched the real distribution of eccentricities.
So what does this mean? It means that on average, about 4% of the known single exoplanets have unseen compaions. For single exoplantes with modest eccentricities, this probability is higher, around 12-16%.
So or solars systm is still unusual, but a little less unusual now,
WHICH RADIAL VELOCITY EXOPLANETS HAVE UNDETECTED OUTER COMPANIONS? Timothy J. Rodigas et al 2009 ApJ 702 716-723 doi: 10.1088/0004-637X/702/1/716 (pre-print here)
Labels: exoplanet, extrasolar planet, peer-reviewed research
Friday, August 28, 2009
Fog Alert on Titan
Image Credit: Mike BrownMike Brown, the discoverer of Pluto-killing Eris, has discovered fog on Titan. This is an amazing discovery as it implies there are large quantities of liquid methane on Titans surface. We have long suspected this (and a lot of the dark patches on Titan are suspected to be methane lakes), but confirmation is pretty stunning.
Read Mike's blog for the details (Mike Brown has a Blog! It's going in my Blog Roll!), and links to his paper. (Hat tip to the Bad Asytomomer, whose own post on this should be read attentively too.)
Labels: peer-reviewed research, Titan
Thursday, August 27, 2009
WASP-18b, the Red Hot Planet of Doom
WASP-18b as visualized in Celestia.When first discovered, "Hot Jupiters", giant exoplanets that orbited their stars more closely than Mercury orbits the Sun, were a source of amazement. 373 planets and 149 Hot Jupiters later close orbiting planets are a bit ho-hum.
Not so WASP-18b. Discovered by the Wide Angle Search for Planets, this amazing planet screams around its sun, HD 10069, in just under an Earth day. From WASP-18b's surface HD 10069 would occupy 30% of its sky (if you could see the sky from its surface). At over 7 times more dense than Jupiter, it probably has a large rocky core.
But it is so massive, and so close to its sun that WASP-18b that it should raise a tidal bulge on its sun, which should slow the planet down and make it spiral into its sun.
And there's the rub. WASP-18b should come close enough to HD 10069 to be torn apart in around 650,000 years. The likelihood that we would come across a planet so close to its death dive is quite remote, either we have been extraordinarily lucky in coming across WASP-18b, or there is something wrong with our theories of tidal dissipation in extrasolar systems. Either way, WASP-18b is a planet that will keep astronomers talking for some time.
Other discussions of WASP-18b at Sky and Telescope and ScienceNow!
If you want to add WASP-18b to Celestia, cut and paste the parameters below to a file and save it as WASP18b.ssc it the extras folder of Celestia, or download WASP18b.ssc to the extras folder.
=====================8<=cut===================================
"b" "HD 10069"=====================8<=cut=================================== The original paper is An orbital period of 0.94 days for the hot-Jupiter planet WASP-18b, Nature, August 27, 2009, by Coel Hellier, D. R. Anderson, A. Collier Cameron, M. Gillon,4, L. Hebb, P. F. L. Maxted1, D. Queloz, B. Smalley, A. H. M. J. Triaud, R. G. West, D. M. Wilson, S. J. Bentley, B. Enoch, K. Horne, J. Irwin, T. A. Lister, M. Mayor, N. Parley, F. Pepe, D. L. Pollacco, D. Segransan, S. Udry & P. J. Wheatley
# WASP-18b Closest known exoplanet to star
# Detected via transit as well as radial velocity methods; from transit
# duration, inclination is 86 degrees, so mass can be determined.
# From transit dimming, radius is estimated at 1.11 jupiters.
{
Texture "exo-class4.*"
NightTexture "exo-class4night.*"
Color [0 0.36 1]
Albedo 0.05
Mass 3274 # M.sin(i) = 10.3 jupiters
Radius 79070
InfoURL "http://vo.obspm.fr/exoplanetes/encyclo/star.php?st=HD+10069"
EllipticalOrbit {
Period 0.0026
SemiMajorAxis 0.02026
Eccentricity 0.0092
Inclination 86
ArgOfPericenter -96
}
Obliquity 82 # guess, to match inclination
#EquatorAscendingNode 96 # guess, to match ascending node
# likely to be in captured synchronous rotation
}
AltSurface "limit of knowledge" "HD 10069/b"
{
Texture "extrasolar-lok.*"
}
Labels: celestia, exoplanet, extrasolar planet, peer-reviewed research
Saturday, December 06, 2008
Echos of Anchient Light - Tycho Brahe's Supernova revelaed
In 1572 astronomer Tycho Brahe saw a new star burst into the sky. This "New Star", Supernova 1572, changed how we say the heavens, and help sweep away the Aristotelian models of the Universe.
This supernova was classified as a type Ia. However, there has been some doubt about this classification, as naturally enough astronomers were not able to directly measure the Supernovas spectrum. Now, over 400 years later, astronomers have been able to measure this spectrum from light echoes reflected from dust clouds and confirm it was a type Ia supernova.
Once the light of the supernova swept past earth back in 1572, it kept going. When it hit dust or gas, some of this light was reflected back to us. These (very) dim reflections are a sort of time machine that allow us to "watch" the supernova as it happened all those centuries ago and measure its spectrum.
Light echoes have been used before to identify supernova (see here and here for more detailed explanations and videos. But this is the first time such a historic supernova has been seen.
This research is reported in the current issue of Nature 2008,Volume 456 Number 7222 pp545-674, Tycho Brahe's 1572 supernova as a standard type?Ia as revealed by its light-echo spectrum p617
This study reports an optical spectrum of Tycho Brahe's supernova near maximum brightness, obtained from a scattered-light echo more than four centuries after the direct light of the explosion swept past Earth. It is found that SN 1572 belongs to the majority class of normal type Ia supernovae.
Oliver Krause et al. doi:10.1038/nature07608 (you will need a subscription to read this)
This supernova was classified as a type Ia. However, there has been some doubt about this classification, as naturally enough astronomers were not able to directly measure the Supernovas spectrum. Now, over 400 years later, astronomers have been able to measure this spectrum from light echoes reflected from dust clouds and confirm it was a type Ia supernova.
Once the light of the supernova swept past earth back in 1572, it kept going. When it hit dust or gas, some of this light was reflected back to us. These (very) dim reflections are a sort of time machine that allow us to "watch" the supernova as it happened all those centuries ago and measure its spectrum.
Light echoes have been used before to identify supernova (see here and here for more detailed explanations and videos. But this is the first time such a historic supernova has been seen.
This research is reported in the current issue of Nature 2008,Volume 456 Number 7222 pp545-674, Tycho Brahe's 1572 supernova as a standard type?Ia as revealed by its light-echo spectrum p617
This study reports an optical spectrum of Tycho Brahe's supernova near maximum brightness, obtained from a scattered-light echo more than four centuries after the direct light of the explosion swept past Earth. It is found that SN 1572 belongs to the majority class of normal type Ia supernovae.
Oliver Krause et al. doi:10.1038/nature07608 (you will need a subscription to read this)
Labels: peer-reviewed research, supernova
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