This week Space Carnival is at Green Gabbro.
There are stories on Planets and Pluto, rocks in space, stargazing (I got an article there), science in space and space exploration.
Have a good time reading.
3 Super-Earths found around a Star
•June 19, 2008 • Leave a CommentSuper-Earth is a planet more massive than our Earth but less massive than Uranus or Neptune (about 15 Earth’s masses).
And astronomers at the ESO La Silla Observatory recently announced that they have found not only one, but three super-Earths orbiting a star 42 light-years away.
This star is called (boringly) HD40307. It is a K-type star, a rather normal one slightly less massive and cooler than our Sun, located in the southern constellation Pictor.
The three super-Earths are 4.2, 6.7 and 9.4 times the mass of our Earth. Their orbital periods are 4.3, 9.6 and 20.4 days respectively, very very short compared to the ~365-day period of our planet, which suggest that they orbit very closely to their parent star. It must be very very hot there…
How do the astronomers found the planets?
By using a technique called Doppler shift. Doppler shift is the change in wavelength and frequency of a source due to the movement of the source itself or the observer or both.
The most frequent example of Doppler effect in our daily life is an ambulance’s siren. As the ambulance approaches us, the wavelengths of the sound are “squeezed” and become smaller, the frequency increases and we hear a higher pitch. Since blue wavelength is smaller than red wavelength, we say that the radiation is “blueshifted”.
The opposite of blueshift is redshift. As the ambulance passes and moving away from us, the wavelengths now are stretched out and become longer, the frequency decreases, so we hear a lower pitch.
Now we look at a star-planets system and see how Doppler shift can be used to detect the planets.
In a star-planet system (or any two-body system), the planet does not orbit the centre of the star but instead both the planet and star orbit their common centre of mass, which is not exactly at the centre of the star. Since the mass of a planet compared to its parent star is so small, the centre of mass actually lies inside the star. So, that why for simplicity we just say the planet orbits the star.
As the star and planet orbit about their common centre of mass, the planet tugs on the star gravitationally and causes the star to wobble. If the wobble is towards us, we see the light from the star is blueshifted; and when the wobble is away from us, the light is redshifted. By analysing the Doppler shift in the spectrum of starlight, these slight changes in the star’s velocity can be detected on Earth. This information can then be used to deduce the planet’s mass and orbit.
This is called the radial velocity method. In this method, the motion of the wobble can only be detected in the direction toward and away from us or the radial direction, hence the name.
The amount of wobble depends on the distance from the star and the mass of the planets. More massive means more wobble and more wobble means easier to detect. Also the nearer the planet to the star, the faster it moves, thus causing larger shift in the star’s spectrum. That’s why most of the extrasolar-planets (planets outside the Solar System, exoplanets for short) found are giant, massive planets, with orbits very close to their parent stars – the hot jupiters.
However, things are changing now.
The wobbles caused by the three newly found super-Earths are really tiny, they induce a motion of their parent star only a few metres per second, and only the high sensitivity of HARPS spectrograph on ESO’s 3.6-m telescope at La Silla made it possible to detect them.
“With the advent of much more precise instruments such as the HARPS, we can now discover smaller planets, with masses between 2 to 10 times the Earth’s mass.” The analysis of all the stars studied with HARPS shows that one solar-like star out of three has either super-Earth or Neptune-like planets with orbital periods shorter than 50 days.
And that is only the super-Earths planets. We have not yet talk about Earth-like planets out there waiting to be discovered. Adding all that to the Jupiter-like planets already known, we may found that planets are very common after all.
Source: ESO Science Release
Stargazing at USM on 20 & 21-Jun
•June 19, 2008 • Leave a CommentUniversiti Sains Malaysia (USM), Penang is organising stargazing party this coming weekend in conjunction with “Young Scientists Carnival and Exhibition”.
Date: 20 and 21-06-2008 (Fri & Sat)
Time: evening
Venue: Outside USM Museum and Gallery. Map to USM. Map inside USM.
For more details, please contact Dr. Chong Hon Yew 016-3157318.
Common Stargazing Terms #3
•June 17, 2008 • 12 CommentsFrom our perspective on Earth, as celestial objects move around our sky, it can be very interesting. They can be seen directly opposite each other, or appear in the same part of the sky, or passing in front of another or even blocking the one behind it from our view.
And we have names for all that situations…
Opposition
Opposition comes from the word opposite. During an opposition, a planet is located at the opposite side of the Sun as seen from Earth. This happens when the Sun, Earth and the planet are in a straight line with our Earth lying in between.
During opposition, a planet is visible in the east once the Sun sets in the west, and can be observed the entire night until the next morning. When the Sun rises in the east, only then the planet sets in the west. Also, this is the best time to observe a planet because it will appear bigger and brighter.
Inferior planets (Mercury and Venus) will never have opposition because that’s no way our Earth can be located between them and the Sun.
Conjunction
Conjunction in simple words means “meeting” of two celestial bodies in our sky. As seen from Earth, these two objects appear near one another in the sky. They appear near only because of our perspective. In reality, they are very far apart in space.
It can be conjunction of the Sun and a planet (during this time we cannot see that planet because it is in the same direction in the sky as the Sun), or conjunction between two planets (such as Venus and Saturn), or between our Moon and a planet.
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Occultation
When a more distant object is blocked by the movement of a nearer object across our line of sight, we called that an occultation. Occultation is a kind of conjunction.
There are so many types of occultation; occultation of stars by our Moon, occultation of planets by our Moon, occultation of a star by a planet, occultation of a planet by a planet etc. If you are interested in the events of occultation, then visit The International Occultation Timing Association.
Occultations can be important events, because they can reveal much information about the objects involved, such as details may be determined of any possible traces of atmosphere of the nearer body.
An example is the discovery of Uranus’ ring system during observations of a stellar occultation by the planet. Actually the observations were planned to use the occultation event to study the planet’s atmosphere. Instead, they found rings around the planet.
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Transit
Transit happens when a smaller celestial body or its shadow passes across the disk of a larger celestial body, whereby it is unable to totally cover the object behind it.
Mercury Transit or Venus Transit is such example. As Mercury or Venus passes in front of the Sun, and since both are so much smaller compared to the Sun, they only appear as a black dot moving across the solar disc. Another example is the transit of Jupiter’s moons and their shadows across the globe of Jupiter. A rare case is a planet transit in front of another planet.
Transit is also a useful tool in astronomy. For example it can use to determine the composition of a planet’s atmosphere or even be used to detect extrasolar planets.
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Eclipse
An eclipse happens when one celestial object moves into the shadow of another.
The most familiar eclipses are the lunar eclipse and solar eclipse. A lunar eclipse occurs when the Moon moves into the shadow of our Earth.
However, the familiar solar eclipse should be more correctly referred to as an occultation rather than an eclipse. As our Moon moves in front of the Sun, it is blocking out a portion or the whole solar disk. Hence the Moon is occulting the Sun and not eclipsing the Sun. Anyway, that name is stuck so we have to go along with it.
Eclipse is not only limited to our Earth-Moon-Sun system. An eclipse also happens when a moon moving into the shadow cast by it parent planet or a moon passing into the shadow of another moon. These events can be quite easily observed within the Jupiter’s system.
Carnival of Space #58
•June 13, 2008 • Leave a CommentCarnival time again.
This week at Universe Today. As usual, lots of articles to keep you busy reading.
Some updates on Phoenix…
•June 13, 2008 • 3 CommentsAfter a successful landing last month, Phoenix is now ready to analyse some Martian soil.
It was an eventful week for Phoenix: after digging up some soil, the sample was sent to the oven of the Thermal and Evolved-Gas Analyzer, or TEGA, which will “bake and sniff” the chemical make-up of the soil.
But somehow, although picture clearly shown that the sample scattered over the oven door and the vibration plate appears to be functioning, a sensor inside the chamber has reported seeing nothing falling into the oven. This may be due to the screen on top of TEGA which only allow small particles into the chamber.
So, the engineers try a revised method – the sprinkle technique – and it seems to work.
After vibrating the screen for three days, the Martian soils now finally “sit” within TEGA. TEGA is ready to heat the soil, and soon we will know what the Martian soils are made of.
Pluto is a Plutoid
•June 12, 2008 • 1 CommentPluto was a planet, before 24 Aug 2006.
Then it was demoted on that day, to a dwarf planet.
Now the International Astronomical Union (IAU) has decided on a new name for dwarf planets like Pluto – the Plutoids.
Definition?
Plutoids are celestial bodies in orbit around the Sun and further away than Neptune and assume a near-spherical shape and have not cleared the neighbourhood around their orbit.
Plutoids’ moons are not plutoids, even if they are a sphere.
Currently the members are Pluto and Eris. Ceres, another dwarf planet, is not a plutoid because it doesn’t locate beyond Neptune. It is located between Mars and Jupiter in the asteroid belt.
Plutoid… what a name! Why not “Erisoid”, since Eris is the larger of the two.
Whatever…
My Dark Sky 
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