Planets around other Stars

Did you know that about 200 planets have been discovered around distant stars? The first planet found to be orbiting a star like our Sun was announced in 1995. Since then astronomers have continued to find new planets outside of our solar system, at a rate of more than one new planet every month!

Artist's concept of a rocky planet in orbit around a distant star.

The star and its planet orbit around each other. The planet moves in a wide orbit, while the star just appears to wobble slightly. By measuring the Doppler shift of the light coming from the star, scientists can detect the tiny motion caused by the planet. Most of the distant planets were discovered this way.

If we are lucky, some of the planets can pass in front of their star. This blocks out some of the light that we usually see from the star, briefly making it dimmer. It's like a solar eclipse, but the planet only covers a small part of the star. Only a few planets outside our solar system pass in front of their stars.

All of the distant planets are too far away to see directly. We can only see their effect on the star that they orbit.

Strange Stuff In Space

There is some pretty strange stuff in space. Things which are unlike anything that anyone sees every day on Earth. Things that challenge our ideas about the Universe. Things that are just so weird that even astrophysicists don't know what they are.

The doomed star Eta Carinae, it is blowing itself apart before it finally goes supernova

When stars die they go out in many different ways. When average mass stars, like our sun, die they go by throwing off their outer layers and leaving behind a White Dwarf. When very massive stars die they often blow themsleves apart in a huge explosion called a Supernova. Depending on how massive a star was that went supernova, a Neutron Star or a perhaps a Black Hole may be left behind as a monument to its former glory.

There are still stranger things in space. Not very long ago astronomers were baffled by the mystery of Quasars. These objects look like stars but are much farther away than stars in our galaxy and they are much more luminous than entire galaxies.

There is also a phenomenon (no, not John Travolta) that has caused much excitement and wonder among astronomers called Gravitational Lensing. This is where massive objects, like galaxies and galaxy clusters, actually bend light like a lens, using gravity! Is that wacky or what!?

One of the strangest things in space is the mystery of Gamma Ray Bursts. These are what seem to be random bursts of gamma rays, you know the radiation that transformed Bruce Banner into the Incredible Hulk. They come from every direction in the sky, they never repeat, and they may indicate the most energetic processes ever seen.

Top 10 Pieces of Evidence For Extra-Terrestial Life

If you are looking for intelligent life beyond our planet here are 10 controversial pieces of evidence for extraterrestrial life:

1. 1976, The Viking Mars landers detect chemical signatures indicative of life

2. 1977, The unexplained extraterrestrial “Wow!” signal is detected by an Ohio State University radio telescope

3. 1996, Martian “fossils” are discovered in meteorite ALH80041 from Antarctica

4. 2001, A more rigorous estimate of the “Drake equation” suggests that our galaxy may contain hundreds of thousands of life-bearing planets

5. 2001, The red tinge of Jupiter’s moon Europa proposed to be due to frozen bits of bacteria, which also helps explain the mysterious infrared signal it gives off

6. 2002, Russian scientists argue that a mysterious radiation-proof microbe may have evolved on Mars

7. 2002, Chemical hints of life are found in old data from Venus probes and landers. Could microbes exist in Venusian clouds?

8. 2003, Sulphur traces on Jupiter’s moon Europa may be the waste products of underground bacterial colonies

9. 2004, Methane in the Martian atmosphere hints at microbial metabolism

10. 2004, A mysterious radio signal is received by the SETI project on three occasions - from the same region of space

Classification of Asteroids

Asteroids are classified into a number of types according to their spectra (and hence their chemical composition) and albedo:

• C-type, includes more than 75% of known asteroids: extremely dark (albedo 0.03); similar to carbonaceous chondrite meteorites; approximately the same chemical composition as the Sun minus hydrogen, helium and other volatiles;
• S-type, 17%: relatively bright (albedo .10-.22); metallic nickel-iron mixed with iron- and magnesium-silicates;
• M-type, most of the rest: bright (albedo .10-.18); pure nickel-iron.
• There are also a dozen or so other rare types.

Because of biases involved in the observations (e.g. the dark C-types are harder to see), the percentages above may not be representative of the true distribution of asteroids. (There are actually several classification schemes in use today.)

There is little data about the densities of asteroids. But by sensing the Doppler effect on radio waves returning to Earth from NEAR owing to the (very slight) gravitational tug between asteroid and spacecraft, Mathilde's mass could be estimated. Surprisingly, its density turns out to be not much greater than that of water, suggesting that it is not a solid object but rather a compacted pile of debris.

Asteroids are also categorized by their position in the solar system:

• Main Belt: located between Mars and Jupiter roughly 2 - 4 AU from the Sun; further divided into subgroups: Hungarias, Floras, Phocaea, Koronis, Eos, Themis, Cybeles and Hildas (which are named after the main asteroid in the group).
• Near-Earth Asteroids (NEAs): ones that closely approach the Earth
  • Atens: semimajor axes less than 1.0 AU and aphelion distances greater than 0.983 AU;
  • Apollos: semimajor axes greater than 1.0 AU and perihelion distances less than 1.017 AU
  • Amors: perihelion distances between 1.017 and 1.3 AU;
• Trojans: located near Jupiter's Lagrange points (60 degrees ahead and behind Jupiter in its orbit). Several hundred such asteroids are now known; it is estimated that there may be a thousand or more altogether. Curiously, there are many more in the leading Lagrange point (L4) than in the trailing one (L5). (There may also be a few small asteroids in the Lagrange points of Venus and Earth (see Earth's Second Moon) that are also sometimes known as Trojans; 5261 Eureka is a "Mars Trojan".)

Between the main concentrations of asteroids in the Main Belt are relatively empty regions known as the Kirkwood gaps. These are regions where an object's orbital period would be a simple fraction of that of Jupiter. An object in such an orbit is very likely to be accelerated by Jupiter into a different orbit.

Asteroids

The first asteroid to be discovered, Ceres, is the largest asteroid known to date and is now classified as a dwarf planet. All others are currently classified as small solar system bodies. The vast majority of asteroids are found within the main asteroid belt, with elliptical orbits between those of Mars and Jupiter. It is thought that these asteroids are remnants of the protoplanetary disc, and in this region the accretion of planetesimals into a larger planet or planets during the formative period of the solar system was prevented by large gravitational perturbations by Jupiter. Some asteroids have moons or are found in co-orbiting pairs known as binary systems.

253 Mathilde, a C-type asteroid.

Asteroids, also called minor planets or planetoids, are a class of astronomical objects. The term asteroid is generally used to indicate a diverse group of small celestial bodies in the solar system that orbit around the Sun. 'Asteroid' (Greek for "star-like") is the most commonly used word in the English literature for minor planets, which has been the term preferred by the International Astronomical Union; some other languages prefer planetoid (Greek: "planet-like"), because it more or less describes what they are. In late August 2006, the IAU introduced the term "small solar system bodies" (SSSB), which includes most objects thus far classified as minor planets, as well as comets. At the same time they introduced the term 'dwarf planet' for the largest minor planets. This article deals specifically with the minor planets that orbit in the inner solar system (roughly up to the orbit of Jupiter). For information on other types of objects, such as comets, Trans-Neptunian objects, and centaurs, see Small solar system body.