Mars, methane and mysteries

Mars may not be as dormant as scientists once thought. The 2004 discovery of methane means that either there is life on Mars, or that volcanic activity continues to generate heat below the martian surface. ESA plans to find out which it is. Either outcome is big news for a planet once thought to be biologically and geologically inactive.

The methane mystery started soon after December 2003, when ESA’s Mars Express arrived in orbit around the red planet. As the Planetary Fourier Spectrometer (PFS) began taking data, Vittorio Formisano, Istituto di Fisica dello Spazio Interplanetario CNR, Rome, and the rest of the instrument team saw a puzzling signal. As well as the atmospheric gases they were anticipating, such as carbon monoxide and water vapour, they also saw methane.

“Methane was a surprise, we were not expecting that,” says Agustin Chicarro, ESA Mars Lead Scientist. The reason is that on Earth much of the methane in our atmosphere is released by evolved life forms, such as cattle digesting food. While there are ways to produce methane without life, such as by volcanic activity, it is the possible biological route that has focused attention on the discovery.

The Mars Express detection of methane is not an isolated case. While the spacecraft was en route, two independent teams of astronomers using ground-based telescopes started to see traces of methane. After five years of intensive study, the suite of observations all confirmed the discovery and presented planetary scientists with a big puzzle.

Methane is thought to be stable in the martian atmosphere for around 300 years. So, whatever is generating the methane up there, it is a recent occurrence. In January 2009, a team led by Michael Mumma of NASA’s Goddard Space Flight Center published results that the methane they saw in 2003 was concentrated in three regions of the planet. This showed that the methane was being released at the present time and was being observed before it had time to distribute itself around the planet.

Things then took a strange turn. Instead of taking 300 years to disappear, the methane had almost entirely vanished by early 2006. Clearly something unusual is going on at Mars. “We thought we understood how methane behaved on Mars but if the measurements are correct then we must be missing something big,” says Franck Lefèvre, Université Pierre et Marie Curie, CNRS, Paris and a member of Mars Express’s SPICAM instrument team.

Together with his colleague François Forget, Mars Express Interdisciplinary Scientist in charge of atmospheric studies and also of Université Pierre et Marie Curie, CNRS, Paris, Lefèvre has investigated the disappearance using a computer model of Mars’ climate. “We have tackled the problem as atmospheric physicists, without worrying about the nature of the source of the methane,” he says.

In results published last week they found that, while their computer model can reproduce atmospheric species such as carbon monoxide and ozone, it is unable to reproduce the behaviour of the methane. “Something is removing the methane from the atmosphere 600 times faster than the models can account for,” says Lefèvre. “Consequently, the source must be 600 times more intense than originally assumed, which is considerable even by Earth’s geological standards.”

To remove methane at such a rate, suspicion falls on the surface of the planet. Either the methane is being trapped in the dust there or highly reactive chemicals such as hydrogen peroxide are destroying it, as was hinted by the Viking missions in the 1970s. If the latter, then the surface is much more hostile to organic molecules (those containing carbon) than previously thought. This will make searching for traces of past or present life much tougher and future rovers will have to drill below the martian surface to look for signs of life.

To help get to the bottom of the methane mystery, ESA and the Italian space agency (ASI) are to hold a three-day international workshop in November. The assembled scientists will discuss the results and plan strategies for the future study of methane. At the workshop, the Mars Express PFS team hopes to present a global map of martian methane. “We have made the PFS mapping a priority over the last few months,” says Olivier Witasse, ESA Project Scientist for Mars Express.

In July, ESA agreed with NASA to launch joint missions to Mars. The topic of methane is of such importance that it will be most likely addressed in these future missions. “Understanding the methane on Mars is one of our top priorities,” says Witasse.

However the methane is eventually explained, it makes Mars a more fascinating place than even planetary scientists dreamed.

Source: ESA

Astronomer Found Planetary Nebula Around Heavy Stars

Lead image caption: An optical image from the 0.6-m University of Michigan/CTIO Curtis Schmidt telescope of the brightest Radio Planetary Nebula in the Small Magellanic Cloud, JD 04. The inset box shows a portion of this image overlaid with radio contours from the Australia Telescope Compact Array. The planetary nebula is a glowing record of the final death throes of the star. (Optical images are courtesy of the Magellanic Cloud Emission Line Survey (MCELS) team).

Planetary nebula – the glowing gaseous shells thrown off by stars during the latter stages of their evolution – were thought to only form around stars the size of our Sun or smaller. Although astronomers had predicted these shells should form around "heavier" stars, none had ever been detected. Until now. An international team of scientists have discovered a new class of object which they call “Super Planetary Nebulae,” found around stars up to 8 times the mass of the Sun.

“This came as a shock to us,” said Miroslav Filipovic from the University of Western Sydney “as no one expected to detect these object at radio wavelengths and with the present generation of radio telescopes. We have been holding up our findings for some 3 years until we were 100% sure that they are indeed Planetary Nebulae”.

The team surveyed the Magellanic Clouds, the two companion galaxies to the Milky Way, with radio telescopes of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Australia Telescope National Facility. They noticed that 15 radio objects in the Clouds match with well known planetary nebulae observed by optical telescopes.

The new class of objects are unusually strong radio sources and are associated with larger original stars (progenitors), up to 8 times the mass of the Sun. The nebular material around each star may have as much as 2.6 times the mass of the Sun.

Filipovic's team argues that the detections of these new objects may help to solve the so called “missing mass problem” – the absence of planetary nebulae around central stars that were originally 1 to 8 times the mass of the Sun. Up to now most known planetary nebulae have central stars and surrounding nebulae with respectively only about 0.6 and 0.3 times the mass of the Sun but none have been detected around more massive stars.

Some of the 15 newly discovered planetary nebulae in the Magellanic Clouds are 3 times more luminous than any of their Milky Way cousins. But to see them in greater detail astronomers will need the power of a coming radio telescope – the Square Kilometre Array planned for the deserts of Western Australia.

Source: Universetoday

Hubble Ultra Deep Field in 3-D

Pernahkan Anda mendengar tentang Hubble Ultra Deep Field Image? Jika belum, silakan simak sedikit penjelasan dari wikipedia.

The Hubble Ultra Deep Field, or HUDF, is an image of a small region of space in the constellation Fornax, composited from Hubble Space Telescope data accumulated over a period from September 24, 2003 through January 16, 2004. It is the deepest image of the universe ever taken, looking back approximately 13 billion years, and it will be used to search for galaxies that existed between 400 and 800 million years after the Big Bang.The HUDF image was taken in a section of the sky with a low density of bright stars in the near-field, allowing much better viewing of dimmer, more distant objects. The image contains an estimated 10,000 galaxies.

Located southwest of Orion in the Southern-Hemisphere constellation Fornax, the image covers 11.0 square arcminutes. This is just one-tenth the diameter of the full moon as viewed from Earth, smaller than a 1 mm by 1 mm square of paper held 1 meter away, and equal to roughly one thirteen-millionth of the total area of the sky. The image is oriented such that the upper left corner points toward north (-46.4°) on the celestial sphere.

Contents
The HUDF is the deepest image of the universe ever taken and it will be used to search for galaxies that existed between 400 and 800 million years after the Big Bang (redshifts between 7 and 12). The star near the center of the field is USNO-A2.0 0600-01400432 with apparent magnitude of 18.95.

The field imaged by the ACS contains over 10,000 objects, the majority of which are galaxies, many at redshifts greater than 3, and some that probably have redshifts between 6 and 7. The NICMOS measurements may have discovered galaxies at redshifts up to 12.

Scientific results

1. High rates of star formation during the very early stages of galaxy formation, under a billion years after the Big Bang.
2. Improved characterization of the distribution of galaxies, their numbers, sizes and luminosities at different epochs, allowing investigation into the evolution of galaxies.
3. Confirmation that galaxies at high redshifts are smaller and less symmetrical than ones at lower redshifts, showing the rapid evolution of galaxies in the first couple of billion years after the Big Bang.

(untuk informasi lebih lengkap tentang HUDF, silakan lihat di artikel ini dan untuk peta dari HUDF, silakan klik link ini.)

Berikut juga ditampilkan sebuah video untuk visualisasi HUDF.

Semoga bermanfaat.

Soal Latihan Astrofisika

Selamat mencoba beberapa soal yang dapat Anda download lewat link berikut:

Soal Latihan Astrofisika - 15 Juni 2009

Selamat belajar.

First Extra-Galactic Planet Spotted in Andromeda

A star in the Andromeda galaxy has a "companion" with six times the mass of Jupiter.

There's no end to the ingenuity of these astronomers.

We've now spotted some 300 extra-solar planets, with rate of discovery increasing at an extraordinary rate. Astronomers have only seen one of these planets directly; the rest have all been inferred because of the effect that they have on their parent stars: changing their brightness or making them wobble. Of course, you have to be able to see the stars to do this kind of work, so astronomers can only see extra-solar planets in our local region of the Milky Way.

Until now. Gabriele Ingrosso at the National Institute of Nuclear Physics, in Italy, and pals say that there is a way to spot planets in other galaxies. The trick is to exploit a phenomenon called microlensing in which the gravity of one star focuses the light from a more distant one toward Earth.

The advantage of microlensing is that it works best for more distant objects, so it's ideal for planet hunting in other galaxies. In theory, it should be possible to see Earth-size objects in this way. The disadvantage is that microlensing is a relatively rapid, one-off event that lasts a few days at most. That makes observations difficult to verify.

It's hard to see individual stars like this, let alone planets. Astronomers have so far spotted only about a dozen stars in Andromeda in this way, and plans are afoot to search for lots more.

But get this: the light from one of these Andromedan stars showed a distinct variability that the discoverers attribute to an orbiting companion.

And today, a new analysis from Ingrosso and co shows that this companion has a mass about six times that of Jupiter. That's heading into brown-dwarf territory, but it's also well within planetary territory too.

Which means that we may well have seen our first extra-galactic planet.

Source : Tecnology Review

Original reference : Pixel-lensing as a way to detect extrasolar planets in M31.

Soal-soal Latihan

Berikut ini ditampilkan beberapa soal "kelas berat". Silakan dicoba dan didiskusikan dengan teman atau guru di sekolah Anda.

1. Having observed the sunrise every day in the same location, the astronomer noticed that the azimuth of the sunrise point changes in the range of 90° during the year. Please find the latitude of the observation place. The refraction and solar disk size can be neglected.
2. Two stars have the same physical parameters. They are observed close to each other in the sky, but their distances are different. Both stars and the observer are situated inside the uniform cloud of interstellar dust. The photometric measurements of these stars in B band gave the results 11m and 17m, in V band the results were 10m and 15m. What is the ratio of distances to these stars? Assume that the extinction property of interstellar dust is proportional to the wavelength in the degree of (–1.3).
3. The magnitude of total umbral lunar eclipse is equal to 1.865. Please find the duration of totality. The expansion of the umbra caused by atmosphere can be disregarded
4. The radius of the Galaxy is equal to 15 kpc, the thickness of its disk being many times less. The mass of the galaxy is equal to 1011 solar masses and it is distributed uniformly in the volume of the galaxy. Two stars are rotating around the center of the galaxy in the same direction by the circular orbits with radii equal to 5 kpc and 10 kpc. Please find the synodic period of the first star while observing from the vicinity of the second star.
5. The white dwarf with radius 6000 km, surface temperature 10000 K and mass equal to solar one moves through the interstellar cluster of comet cores, each one has radius 1 km and density 1 g/cm3. How many comets must fall on the white dwarf every day to increase its luminosity in two times?

Selamat belajar

Resensi Buku : Menjelajah Tata Surya

Format: Paperback, 302 halaman
Penerbit: Kanisius
Pengarang: A. Gunawan Admiranto
Harga : Rp.60.000,00
isbn: 9789792119
Tanggal Publish: 31 Mar 2009

Alam semesta telah sejak lama memukau manusia dengan keindahannya dan juga misteri di dalamnya. Dan perjalanan sejarah manusia membuktikan kalau keingintahuan untuk menyingkap misteri di alam semesta telah membawa manusia dalam perjalanan panjang penelitian dan penjelajahan untuk mengungkap satu demi satu misteri yang menyelimuti alam maha luas.

Dari penglihatan akan gerak benda langit dari Bumi sampai penjelajahan telah dilakukan oleh manusia demi menyingkap misteri itu. Buku karangan Gunawan Admiranto, :Menjelajah Tata Surya”, mencoba membawa kita mengenal ruang lingkup Tata Surya dimulai dari sejarah perkembangan konsep Tata Surya sampai dengan anggota keluarga yang ada di tepian luar Tata Surya.

Perjalanan di tata Surya diawali dari Matahari kemudian ke setiap planet dan diakhiri dengan keberadaan obyek-obyek di tepi luar Tata Surya yang dikenal sebagai obyek Kuiper. Keindahan Tata Surya dipaparkan dengan bahasa yang sederhana untuk dipahami. Satu per satu planet dikupas sampai ke proses yang terjadi di dalamnya. Dan tak lupa definisi planet yang terbaru pun disertakan dengan mengacu pada peristiwa mengapa Pluto bukan planet lagi. Kehadiran klasifikasi baru planet katai juga dijelaskan dengan baik.Buku ini sangat baik untuk para pelajar yang ingin mengenal lebih dekat Tata Surya dan semua yang ada di dalamnya.

Namun bagaimanapun gamblangnya Tata Surya dijelaskan lewat penjelajahan ini, penjelajahan sesungguhnya dari para ilmuwa belumlah berakhir. Masih ada segudang misteri yang masih menanti untuk disingkapkan.

Sumber : langitselatan.com

Buku ini sangat disarankan bagi pecinta astronomi, khususnya para pemula. Saya pernah menggunakan buku ini (edisi lama) dan banyak sekali hal yang dapat dipelajari. Selamat belajar.

Binary Stars

Looking through a telescope at the stars there is very little information we can gain from them. To be sure, we know what color they are and we can see that some are more luminous than others. If we use a spectrograph we can tell what elements they are made up from. From these facts alone, it is difficult to tell just how much mass they contain.

By looking at pairs of stars that orbit one another we can try to answer the question, how much mass do the stars have?

Binary stars can be of two fundamental types:

• Visual Binaries
• Optical Doubles

Alberio (Visual Binary)
Visual Binaries are stars that are clearly gravitational associated with one another. They orbit each other around a common center called the barycenter. Visual binaries can be seen optically through a telescope. Only a small portion of binary stars are visual binaries. In order to see a visual binary, the stars must be separated by fairly wide distances, and the orbital periods are usually very long.

Optical Doubles are stars that appear to lie close together, but in fact do not, they only appear to us from our earthly observation to be close together. One of the stars in the pair is actually behind the first star and very far away. The stars of an optical double are not gravitationally bound.

William Herschel began looking for optical doubles in 1782 with the hope that he would find a measurable parallax, by comparing a close star to the more distant star in an optical double.
Herschel did not find any optical binaries, but he did catalog hundreds of visual binaries. In 1804 Herschel had so many measurements of visual binaries that he concluded that a pair of stars known as Castor were orbiting one another. This was an important discovery, because it was the first time observational evidence clearly showed two objects in orbit around each other outside of the influence of our own Sun and Solar System.

Spectroscopic Binary
It is also possible to detect binary stars using a spectroscope. If two stars are orbiting each other they will both produce a spectrum. If the stars are close to being the same brightness it is possible to see different spectral lines from both stars. These stars are of particular interest because it can be used to determine the radial velocity of the orbit of the two stars. Stars appear red shifted when receding away from the earth and blue shifted as they approach. This effect is caused by the Doppler effect which distorts arriving light waves from the stars depending on the direction if their motion. A Spectroscopic binary will alternate between blue and red shifted spectral lines.


Spectroscopic binaries are not detectable if we are seeing the star head on because no Doppler shifts would be present in the spectrum. If the Doppler shifts are present in a single line of the spectrum, we are seeing the light from only one star and we call this a single-line spectroscopic binary. If we can see the light from both stars the Doppler shifts will alternate, split and merge depending on the positions of the two stars in their orbits. This is called a double-line spectroscopic binary.

One very important detail, we do not know how the orbits of the two stars are inclined to earth. This inclination could be any angle, for that bit of information we have to go back to visual methods in order to see the individual stars to determine the inclination of their orbits relative to earth. Even so we can not for certain determine the true inclination of the orbit so our mass calculation is only a lower limit to the masses of the two stars.

Radial velocities permit astronomers to compute the total mass for the two stars, they do not provide the masses for the individual stars and other methods must be used to make that determination

Eclipsing Binary
Another type of binary called the Eclipsing binary can be studied. The information gathered can be used to calculate the individual stellar masses and the diameters of the individual stars. It is rare to find two stars in orbit around one another to have orbital inclination where the stars pass in front of one another to form one point of light as seen from earth.
When the orbital inclination if the eclipsing binary is edge on to earth, the stars will seem to pass in front of one another as they orbit, when the light from the brighter star is eclipsed we will see a deep decline in the amount of light received from the star (6/25/95 in Figure 1) we call this primary minimum, also when the light from the dimmer star is blocked by the brighter the light received declines again, but not so deep and we call this secondary minimum (see 6/9/95 in Figure 1) , otherwise we are able to collect some or all of the light from both stars.


The pattern of these light changes is called a light curve and the data for it gathered by the use of a photometer, making periodic measurements until the eclipsing binaries produce a complete orbital cycle.

We use the mass vs. luminosity relationship to determine what the difference is between the individual masses, then using the mass of the entire system calculated from the radial velocity information, we can determine what the individual masses of the two stars should be. The photometeric data removes some of the uncertainty in regard to the inclination because the shapes of the light curves will be different for a partial eclipse than for a total eclipse.
ALGOL is one of the best known and most studied eclipsing binary stars. ALGOL is normally about 2.3 magnitude, but every 10 hours or so it will dim to about 3.4 magnitude, in other words ALGOL becomes 68% dimmer. I suspect that humanity has known about ALGOL's behavior for quite some time, since the Arabic name of ALGOL means "Demons Head", and ALGOL is associated with the severed head of Medusa. ALGOL is often referred to as the winking eye of the demon.

An eclipsing binary occurs when the orbital plane of the binary system is exactly When one star passes directly in front of the other, as viewed from Earth, we seen an eclipsing binary perpendicular to the plane of the sky.

Dwarf Nova or Recurrent Nova


When an otherwise normal star is associated with a white dwarf companion, a type of binary called a recurrent nova, or dwarf nova may occur. The normal star transfers mass onto an accretion disk which forms around the white dwarf. As material falls onto the accretion disk some of the material may be transferred to the white dwarf by turbulence in the accretion disk, this causes a sudden brightening of the white dwarf as the hydrogen is converted into helium.
If enough material from the accretion disk falls onto the white dwarf the hydrogen gas will become compressed and will not immediately fuse until a substantial increase in temperature occurs; the material will suddenly and violently erupt fusing into a runaway fusion reaction and a violent eruption called a dwarf nova occurs which will blow the accretion disk away, but it will not disturb the normal star.


Mass transfer will quickly resume and a new accretion disk will form. The cycle will continue until enough mass is drawn off the normal star to halt the reaction.

Mass transfer in any type of binary system will affect the evolutionary cycle of the two stars. The normal star will burn its fuel more slowly as mass is removed and the star cools down due to less internal heating from gravitational forces. It will also accelerate the evolution of the star receiving the mass, for the same reasons, more mass, more internal heating and the hastening of the fusion process.

If the material transfers very quickly, the gravitational forces will prevent the hydrogen from fusing by compressing it even further until the hydrogen gas becomes degenerate matter. Degenerate matter does not expand due to the increases in temperature so the mass of the white dwarf increases until it exceeds the Chandrasekhar Limit. When this happens the white dwarf will collapse and a type I supernova will occur which may destroy the companion star and the white dwarf changes into a neutron star or a black hole.

Burster
A similar event can occur when a normal star is associated with a pulsar, the energy given off will be mostly X-rays however, and instead of being called a dwarf nova or recurrent nova, it is called an X-ray burster or more simply a burster. We think that as normal hydrogen falls onto the accretion disk it is quickly converted into helium, when the helium reaches a depth of 1 meter, it will explosively convert helium into carbon producing X-rays. The longer the delay in fusing carbon, the larger and more violent the burst will be. The main difference between the recurrent nova and the burster is that the accretion disk will be hotter in the burster because it is already fusing hydrogen into helium, also the burst will produce mostly X-rays instead of visible light.


When a black hole is associated with a normal star, it will produce the same events as an X-ray burster and the only way to be sure that the companion is a blackhole, is when the mass of the compact object is greater than 3 solar masses. This is far too much mass for the companion to be a neutron star. The gravitational forces would cause the collapse of the star beyond the point of the neutrons to support themselves against the force of gravity and the star would collapse to a zero radius creating a black hole.

Calculation of star's properties with binary stars
Types of Binaries

• Visual Binary: Can see both stars and follow their orbits over time.
• Spectroscopic Binary: Cannot separate the two stars, but see their orbit motions as Doppler shifts in their spectral lines.
• Eclipsing Binary: Can separate the stars, but see the total brightness drop when they periodically eclipse each other.

Visual Binaries --> Two stars orbiting about their center-of-mass.


Center of Mass
Two stars orbit about their center of mass.

• Measure semi-major axis, a, from projected orbit & the distance.
• Relative positions about the center give: M1/M2 = a2/a1

Measuring Masses
Newton's Form of Kepler's Third Law:
Procedure:
1. Measure the period, P, by following the orbit.
2. Measure semi-major axis, a, and the Mass Ratio, M1/M2, from the projected orbit on the sky.
3. Solve the equation above and separate Masses.

Problems
We need to follow an orbit long enough to trace it out in detail:

• This can take decades
• Need to work out the projection on the sky

Measurements depend on knowing the distance:

• semi-major axis depends on d
• derived mass depends on d^3

Small errors add up quickly (10% error in distance translates into a 30% error in the mass!).


Spectroscopic Binaries
Most binaries are too far away to be able to see both stars separately.
But, you can detect their orbital motions by the periodic Doppler shifts of the spectral lines:

• Determine the orbit period & size from the pattern of orbital velocities


Problems:
Cannot see the two stars separately:

• Semi-major axis must be guessed from the orbit motions.
• Can't tell how the orbit is tilted on the sky

Everything depends critically on knowing the distance.
Again...

Eclipsing Binaries
Two stars orbiting nearly edge-on to our line-of-sight.

• See a periodic drop in brightness as one star eclipses the other.
• Combine with spectra which measure orbital speeds

With the best data, one can find the masses of the stars without having to know the distance!!!


Problems
Eclipsing Binary stars are very rare.
Measurement of the light curves is complicated by details:

• Partial eclipses yield less accurate numbers.
• The atmospheres of the stars soften the edges.
• Close binaries can be tidally distorted.

However, the best masses are from eclipsing binaries.

Source : many different sites