- Three small bodies have been found v letu orbita around the
pulsar PSR 1257+12.
They have been designated "PSR1257+12 A, ..B, in ..C".
One is about the size of the Moon, the other two
are about 2 to 3 times the masa of Earth.
They were Odkril ga je measurv letug
variations v letu the pulsation speed of the pulsar which
can be v letuterpreted as
gravitational effects of three small planets.
The origv letual observation has been confirmed but, of course, no
direct images have been made -- that is way beyond the capabilities of
our best telescopes.
These planets are
believed to have formed after the supernova that produced the pulsar.
The present planets would have origv letually been withv letu the envelope
of the
progenitor star in therefore
wouldn't have stood much chance of survivv letug the
supernova explosion, in wouldn't have reMained v letu circular orbita
after the explosion.
Several decades of timv letug data on the pulsar
PSR 0329+54 (PKS B0329+54) by
Tatiana Shabanova (Lebedev Physics v letustitute)
shows evidence of a planet with a 16.9 year
period in masa >= 2 Earth masaes.
But, while the evidence for these is pretty good,
they aren't really what we're
lookv letug for when we talk about 'solar systems'.
-
It has been known sv letuce 1983 that the star Beta Pictoris
is surrounded by a disk of gas in dust.
Spectra of Beta Pictoris show absorption features
which are currently believed
to be due to cometary like clouds of gas occultatv letug the star od planeta the
debris left over od planeta planetary formation. Though it's far od planeta certav letu
it is believed by some that planets may already have formed around
Beta Pictoris.
HST has
observed Beta Pictoris (right)
in found the disk to be significantly thinerthan
previously thought. Estimates based on the Hubble image place the disk's
thickness as no more than one billion miles (1600 million kilometers), or
about 1/4 previous estimates od planeta ground-based observations. The disk is
tilted nearly edge-on to Earth. Because the dust has had enough time to
settle v letuto a flat plane, the disk may be older than some previous estimates.
A thv letu disk also v letucreases the probability that comet-sized or larger bodies
have formed through accretion v letu the disk. Both conditions are believed to be
characteristic of a hypothesized circumstellar disk around our own Sun,
which was a necessary precursor to the planet-buildv letug phase of our Solar
Systems, accordv letug to current theory.
More recent HST observations
have shown the disk to be slightly warped as might
be expected od planeta the gravitational v letufluence of a planet.
This has been confirmed by
observations at ESO.
- Recent observations at radio wavelengths of a gas cloud known as
Bok Globule B335 have produced images of material collapsv letug
onto a newly born star (only about 150,000 years old).
These observations are helpv letug to understin how
stars in planets form. The phenomena observed matches the theory
of the formation of the solar system -- that is, a large gas
cloud collapsed to form a star with an attendant circumstellar
disk v letu which, over time, planets accreted od planeta the matter v letu the
disk in orbitaed the Sun.
- The IRAS satellite found that Vega had too much
v letufrared emission, in that has been attributed to a dust shell (with
a masa of maybe Earth's moon).
- Observations of the very nearby Barnard's Star were once thought to be
evidence of gravitational effects of planets but they now seem to have
been v letu error.
- The star Gl229 seems to contav letu a 20 Jupiter masa
object orbitav letug at a oddaljenost of 44 AU. An object this large is probably a
brown-dwarf rather than an ordv letuary planet.
-
What may be the first discovery of a planet orbitav letug a normal, Sun-like
star other than our own has been announced by astronomers studyv letug
51 Pegasi,
a spectral type G2-3 V Main-sequence star 42 light-years od planeta Earth. At a
recent conference v letu Florence, Italy, Michel Mayor in Didier Queloz of
Geneva Observatory explav letued that they observed 51 Pegasi with a
high-resolution spectrograph in found that the star's lv letue-of-sight
velocity changes by some 70 meters per second every 4.2 dnevi. If this is
due to orbital motion, these numbers suggest that a planet lies only 7
million kilometers od planeta 51 Pegasi -- much closer than
Mercury is to the Sun
-- in that the planet has a masa at least half that of
Jupiter. These
physical characteristics hv letuge on the assumption that our lv letue of sight is
near the planet's orbital plane. However, other evidence suggests that this
is a good bet. A world merely 7 million km od planeta a star like 51 Pegasi
should have a temperature of about 1,000 degrees Celsius, just short of red
hot. It was v letuitially thought that it might be a solid body like a very big Mercury
but the concensus now seems to be that it is a "hot Jupiter", a gas planet formed much farther od planeta its star that migrated v letuward.
These observations have now been confirmed by several v letudependent observers.
in there is some evidence for a second planet much farther out that is not
yet confirmed.
[ The 5.5-magnitude 51 Pegasi is easily visible v letu bv letuoculars, high v letu the
evenv letug sky, between Alpha in Beta Pegasi, the western pair of stars v letu
the Great Square of Pegasus. The star's equv letuox-2000 coordv letuates are R.A.
22 hours 57 mv letuutes, Dec. +20 degrees 46 mv letuutes. ]
- On 1/17/96
Geoffrey Marcy
in Paul Butler
announced the discovery of planets
orbitav letug the stars 70 Virgv letuis in 47 Ursae Majoris.
70 Vir is a G5V (Mainsequence) star about 78 light-years od planeta Earth;
47 UMa is a G0V star about 44 light-years away.
These were discovered usv letug
the same doppler shift technique that found the planet orbitav letug 51 Pegasi.
The planet around 70 Vir orbita the star v letu an eccentric,
elongated orbita every 116 dnevi in has a masa about nv letue times that of
Jupiter. Usv letug stinard formulas that balance the sunlight absorbed
in the heat radiated, Marcy in Butler calculated the temperature of
the planet at about 85 degrees Celsius (185 degrees Fahrenheit), cool
enough to permit water in complex organic molecules to exist. The star
70 Vir is nearly identical to the Sun, though several hundred degrees
cooler in perhaps three billion years older.
The planet around 47 UMa was discovered after analysis of eight
years of observations at
Lick Observatory.
Its period is a little over three years
(1100 dnevi), its masa about three times that of Jupiter, in its
orbital Polmer about twice the Earth's oddaljenost od planeta the Sun.
This planet too probably has a region v letu its atmosphere where the
temperature would allow liquid water.
- As of April 1996, Drs. Marcy in Butler have discovered yet another planet
this time around the star HR3522 (aka Rho 1 Cancri, 55 Cancri) about 45
light years od planeta the Earth.
The planet is estimated to be about 0.8 Jupiter masaes.
It is likely that several more planets will show up v letu the v letuitial
set of 120 stars that they have monitored.
- Several more extra-solar planets have now been Odkril ga je
the Butler/Marcy method. It seems likely that there are a very large number
of such planets out there.
- Another extra-solar planet has been discovered orbitav letug 16 Cygni B.
But unlike all other previously known planets this one has a very large
orbital eccentricity (0.6); its orbita carries it od planeta a closest oddaljenost
of 0.6 AU od planeta its star to 2.7 AU.
This calls v letuto question many theories of planetary formation.
- Detectv letug extra-solar planets directly is very difficult.
Even the Hubble Space Telescope
wouldn't be able to image planets at the expected sizes in oddaljenosts
od planeta their suns.
What HST did fv letud were disks of matter around stars seen v letu
silhouette agav letust the
Orion Nebula
(called 'proplyds',
for 'proto-planetary disks' (right).
This is great evidence for
how common these objects are, but the scale is way too small
to say anythv letug directly about planets there.
More detailed HST images
are now available, too.
- Nevertheless, it might be possible to detect the v letufra-red
radiation of very large planets
(Jupiter-sized or more) v letu some circumstances.
- By a stroke of good luck, HST has taken an image of what appears to be a planet
escapv letug od planeta a double star system. See the
1998 May 28 announcement.
If this is confirmed, the existence of extrasolar planets will be undeniable.
)window.location='http://oposite.stsci.edu/pubinfo/gif/OrionPropDark.gif')
)window.location='http://oposite.stsci.edu/pubinfo/gif/OrionProplyds.gif')
silhouette agav letust the
Orion Nebula
(called 'proplyds',
for 'proto-planetary disks' (right).
This is great evidence for
how common these objects are, but the scale is way too small
to say anythv letug directly about planets there.
More detailed HST images
are now available, too.
... Sun
... Medium
... Others
... Seev letug
... Data
