How many planets are there today?

Answer 1

HOW MANY ARE KNOWN AT THE MOMENT?:

8 in our solar system + 3 dwarf planets

(Planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus & Neptune) (Dwarf Planets: 1 Ceres, 134340 Pluto, 136199 Eris)

AND IN THE MILKY WAY GALAXY?

Since pulsar planets were discovered in 1992 and 51 Pegasi b was discovered in 1995 we now know a total of 209 orbiting other stars:

Detected by radial velocity method: 169 planetary systems, 197 planets, 20 multiple planet systems.

Detected by microlensing: 4 planets.

Detected by direct imaging: 4 planets.

Pulsar planets: 2 planetary systems, 4 planets, 1 multiple planet system.

See the full list in the Encyclopaedia of Exoplanets (third link) published and maintained by the Paris Observatory. Appropriately as it was the work of Urbain LeVerrier at that observatory that led to the discovery of Neptune in 1846.

WHAT OF THE FUTURE?

Improved detection rates can be expected in the coming years. Principally from CoRoT and the Kepler Mission: which being space-based will avoid the problems the earth's atmosphere creates for ground-based telescopes,

COROT:

On 15th November 2006 the CoRoT spacecraft arrived at the Baikonour launch base,

COROT (COnvection ROtation and planetary Transits) is a space mission approved and led by the French Space Agency (CNES) in conjunction with the European Space Agency and other international partners. The primary objective of COROT will be to search for extrasolar planets, particularly those of large terrestrial size. It is scheduled for launch on December 22, 2006, and will be the first mission of its kind.

COROT consists of a 27 cm in diameter afocal telescope with an array of spectroscopic detectors. The satellite has a launch mass of 630 kg, is 4.10 metres long, 1.984 metres in diameter and powered by two solar panels.

A Russian rocket will lift the satellite into a circular polar orbit with an altitude of 827 km. Over its planned 2½ years mission it will observe perpendicular to its orbital plane meaning there will be no Earth occultations, allowing 150 days of continuous observing. During the northern Summer it will observe in an area around Serpens Cauda and during the Winter it will observe in Monoceros. Between this observing periods for 30 days, COROT will observe 5 other patches of the sky.

The probe will monitor the brightness of stars, watching for the slight dimming that happens in regular intervals when planets transit their primary. COROT will be sensitive enough to detect rocky planets, though only those several times larger than Earth; it is also expected to discover new gas giants, which comprise almost all of the known extrasolar planets.

COROT will also undertake asteroseismology. It can detect luminosity variations associated with acoustic pulsations of stars. This phenomenon allows calculation of a star's precise mass, age and chemical composition and will aid in comparisons between the sun and other stars.

In each field of view there will be one main target star for the asteroseismology as well as up to nine other targets. Simultaneously, it will be recording the brightness of 12,000 stars brighter than apparent magnitude 15.5 for the extrasolar planet study. It is expected that a few dozen planets will be found.

THE KEPLER MISSION

The scientific objective of the Kepler Mission, due for launch in 2008, is to explore the structure and diversity of planetary systems. This is achieved by surveying a large sample of stars to achieve several goals:

Determine how many terrestrial and larger planets there are in or near the habitable zone of a wide variety of spectral types of stars

Determine the range of sizes and shapes of the orbits of these planets

Estimate how many planets there are in multiple-star systems

Determine the range of orbit size, brightness, size, mass and density of short-period giant planets

Identify additional members of each discovered planetary system using other techniques

Determine the properties of those stars that harbor planetary systems

The random probability of a planetary orbit being along the line-of-sight to a star is the diameter of the star divided by the diameter of the orbit. For an Earth-like planet at 1 AU transiting a solar-like star the probability is 0.47%, or about 1 in 210; it's slightly larger at 0.72 AU (the orbital distance of Venus), 0.65%; such planets would be Earth-like if the host star is a late G-type star such as Tau Ceti. In addition, because planets in a given solar-system tend to orbit in similar planes, the possibility of multiple detections around a single star is actually rather high. For instance, if an alien Kepler-like mission observed Earth transiting the Sun, there is a 12% chance of also seeing Venus transit.

The Kepler Mission has probably the best chance of detecting Earth-like planets at current technology levels. One important advantage it has is that it is designed to observe 100,000 stars simultaneously. This provides a much better chance for seeing a transit. In addition, the 1 in 210 probability means that if 100% of stars observed had Earth-like terrestrial planets, Kepler would find about 480 of them. The mission is therefore ideally suited to determine the frequency of Earth-like planets around other stars.

I hope that this has stimulated you into reading up on a fascinating subject!

Answer 2

8

Answer 3

8

Answer 4

There are 8 Official planets in the Solar System

Answer 5

how many planets... where?

in our solar system there 8 planets, now that Pluto was downgraded to a dwarf planet (after all it is smaller than our Moon...)

outside our solar system we have just started to scratch the surface but the list is already over 200 planets, and due to reach a few thousands in the next few years thanks to new planet-searching satellites to be launch in the near future

hope this helps

Answer 6

No one knows. There are millions of stars in the universe which are like our sun. They could all have planets that we can't see with our telescopes. I can only speculate. My guess is millions. In our solar system, however, there are 8 actual planets orbiting our sun.

Answer 7

In our galaxy----8.Since Pluto is no longer a planet.
But scientists say that they may have recently found a new planet further than Pluto.It is not yet confirmed whether it is a planet or not.

Answer 8

Nobody knows. Currently, our Sun has eight planets in its little "family" . Our Sun is but one of many billions in our galaxy, and many of the others have already had planets of their own detected by us. Then, there are many billions of galaxies......you get the idea.

Answer 9

Countless but we haven't discovered many of them yet.

The first discovery of a planet orbiting a star similar to the Sun came in 1995. The Swiss team of Michel Mayor and Didier Queloz of Geneva announced that they had found a rapidly orbiting world located blisteringly close to a the star 51 Pegasi. Their planet was at least half the mass of Jupiter and no more than twice its mass. They had observed it indirectly, using the radial velocity method. (For information about radial velocity detection, see "Finding Planets" )

These announcements marked the beginning of a flood of discoveries. Three months later, a team led by Geoffrey W. Marcy and Paul Butler of San Francisco State University and the University of California at Berkeley confirmed the Swiss discovery -- and turned up two more planets. By the end of the 20th century, several dozen worlds had been discovered, many the result of months or years of observation of nearby stars.



Distribution of planets found around nearby stars (Courtesy G. Marcy / E. Williams)

Many, like the companion to 51 Pegasi, are bizarre, with short periods and eccentric orbits close to the star. But more recently, astronomers have found planets that more closely resemble those in our outer solar system, with circular orbits and longer orbital periods.

Astronomers attribute the abrupt surge in discoveries, in part, to technological advances in recent years. These include:

Significant improvements in spectrometers, instruments that separate starlight into its component colors for analysis.
Better electronic sensors that record the incoming starlight collected by telescope optics.
The development of computer software that can reliably discern fluctuations in starlight and the motion induced by the gravitational pull of unseen companions.
Furthermore, the maturation of these technologies has led to intensified searches and data gathering.


A new era of exploration
None of these new worlds has actually been seen. All are massive, Jupiter-class planets, considered unlikely to harbor life as we know it. Many have short orbital periods. If planets like Earth exist, with smaller masses and longer orbital periods, their discovery will require more sensitive instruments and years of precise, sustained observations.

Nonetheless, the dream of other worlds waiting to be explored -- and the idea that our solar system is not unique -- has moved from philosophical speculation into reality. These discoveries harbor the potential to shift human thinking on a scale comparable to the Copernican revolution.

The next chapter in the brief history of extrasolar planet discoveries is already being written. New tools and visionary technologies currently in development will soon enable us to learn more about these nearby planetary systems. The Keck Interferometer will capture the first images of gas giants outsider our solar system, while the Space Interferometry Mission will be capable of detecting evidence of planets slightly larger than Earth. Meanwhile, other ground-based planet search programs continue to yield new discoveries, giving scientists a broader view of the diversity of planets in our galaxy.

Answer 10

In our solar system, there are eight planets. In the universe, no one knows how many. Millions maybe.

Answer 11

8 planets now in our SOLAR SYSTEM. Pluto was stripped from planetary status a few months ago.