Is it a planet? A meteoroid? An asteroid? No, it's Sedna. And it's a planetoid.
A planetoid is smaller than a planet but bigger than an asteroid. Sedna, which is also known as 2003 VB12, is the largest object discovered in the Solar System in more than 70 years! (The discovery of Pluto, which took place in 1930, was the last.) Sedna's diameter is estimated to be about two-thirds of that of Pluto's or about 1500 kilometers (1000 miles). For comparative purposes, the largest asteroid in the asteroid belt is Ceres, which has a diameter of around 950 kilometers.
Sedna is the coldest place in the solar system.
Sedna was discovered on November 14, 2003. Why hadn't it been detected earlier? Firstly, Sedna is extremely faint with a magnitude of about 20.5. Secondly, Sedna moves quite slowly. Only by using images over a two-year period were astronomers able to determine its orbit. Thirdly, cutting-edge technology was needed in the form of a sophisticated 172 Megapixel CCD camera and the use of a high-speed computer, equipment that was not available until recently.
Sedna also holds the record for being the farthest object observed in the solar system. Currently, it is 13 billion kilometers away, which is 90 times farther away from the Sun than the Earth and more than twice the distance to Pluto. It is so distant that light from the planetoid takes more than 12 hours to reach Earth! Thanks to Mike Brown, Chad Trujillo and David Rabinowitz the astronomers who made the discovery the visible Solar System is now a little bigger.
Artist's Conception of Sedna, Its Possible Moon and the Sun
However, Sedna's orbit is highly elliptical. In about 70 years, it will achieve its closest approach of 75 astronomical units. (One astronomical unit is the Earth-Sun distance of 150 million kilometers or 93 million miles.) Eventually, it will disappear from sight venturing into the darkness of the outermost reaches of the solar system and arrive at an incredible distance of 900 astronomical units or 135 billion kilometers from the Sun, and it will take more than 5000 years for Sedna do this! (It orbits the Sun once every 10,500 years).
Interest in Sedna by astronomers is keen; it sits in "no man's land" beyond the Kuiper Belt that encompasses Pluto and other rocky bodies but inside of the Oort Cloud where many comets originate.
"Red in the face!" This phrase is not a description of an embarrassed astronomer; rather, it refers to Sedna itself. An analysis of its light indicates that the planetoid is almost as red as Mars. Why it is so red is unknown.
Sedna is also the coldest known place in the solar system with a temperature estimated to be about 240 degrees Celsius below zero (-400 degrees Fahrenheit). Its surface is suspected to contain ice in the form of frozen water, methane, carbon dioxide (so-called dry ice) or other gases, since otherwise Sedna would reflect too little light from the Sun to make it visible from Earth. Such ices, however, would not explain the planetoid's red color.
The visible Solar System is now a
Sedna is frigid because very little precious sunlight reaches it: If you were to stand on its surface and view the Sun with an unaided eye, it would appear only as a spectacularly bright star with hardly any disk.
Sedna revolves about its axis rather slowly once every 40 days or so. A possible explanation for this is that its rotation is slowed by a moon. Eventually, observations by the Hubble Space Telescope should confirm or refute this idea.
It is predicted that many more objects like Sedna will be discovered in the coming years since the team that discover Sedna has explored only 15% of the sky. In June 2002, they discovered Quaoar, a body in the Kuiper Belt that has a diameter a little more than half that of Pluto's. Quaoar is the largest of many sizeable Kuiper Belt Objects. So stay tuned soon one previously unexplored region of the solar system will likely be populated by all kinds of strange frozen bodies! And then maybe Pluto will have more siblings beside Sedna.
On June 8, 2004, a dark spot will appear on the Sun. It will slowly move across its face. But it will not be a sunspot. It will be Venus. For the first time since 1882 a period of 122 years Venus will make a solar transit lasting a little more than six hours.
The transit is like an eclipse by a planet rather than the Moon. Because Venus is smaller, it does not block out the Sun.
This relatively rare event can be viewed using mounted binoculars or a telescope and projecting the image of the Sun onto a white card beyond the eyepiece. The Sun will appear as a bright disk, and Venus will be evident as a black circular disk with a diameter of 1/32 of the diameter of the Sun. It may also be possible to see sunspots. The transit begins at 05:13 Universal Time (UT) and ends at 11:25 UT.
Simulation of the Transit
CAUTION: One should *never* directly look at the Sun with or without a lens.
Except in cloudy regions, the entire transit will be visible from Europe and from most of Africa and Asia. Partial viewing of less than 6 hours is possible from Australia (near sunset) and the eastern parts of North and South America. Except for those living in Argentina and Chile, those who are unable to see the 2004 transit will be able to observe at least a partial Venusian transit in June 2012. Regardless of weather or location, it will be possible to see this year's event through the Internet at sites such as those sponsored by the European Southern Observatory.
In the western part of the United States, the best way to experience the transit
is through one of the above webcams. One should go on the Internet on the evening of June 7.
During March and April (of 2004), Venus appears as a "very bright star" in the western sky soon after sunset. In May, Earth's sister planet will be getting closer to the Sun so as to make the transit in early June.
Venusian transits take place only in the months of June and December because of the inclinations of the planes of orbits of Earth and Venus. They also happen regularly with four occurring every 243 years. One takes place in June, then 8 years later in June, then 105 years later in December and then 8 years later in December; 122 years after that the pattern repeats.
Good luck on June 6 and enjoy the solar show!
This page was created by the staff of
an organization devoted to the promotion of
science and scientific education through books, the Internet
and other means of communication.
This web page and its contents may NOT be copied onto other web
sites, but other sites may link to this page.