20000 Varuna facts for kids
Hubble Space Telescope image of Varuna, taken in 2005
|
|
| Discovery | |
|---|---|
| Discovered by | Spacewatch (Robert McMillan) |
| Discovery date | 28 November 2000 |
| Designations | |
| MPC designation | (20000) Varuna |
| Pronunciation | VARR-ə-nə Sanskrit वरुण |
|
Named after
|
Varuna |
| 2000 WR106 | |
| TNO · classical (hot) Scat-Ext |
|
| Adjectives | Varunian |
| Orbital characteristics | |
| Epoch 2025-05-05 (JD 2460800.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 70.28 yr (25,670 days) |
| Earliest precovery date | 24 November 1954 |
| Aphelion | 45.448 AU (6.7989 Tm) |
| Perihelion | 40.827 AU (6.1076 Tm) |
| 42.718 AU (6.3905 Tm) | |
| Eccentricity | 0.0536 |
| 279.21 yr (101,980 d) | |
|
Average orbital speed
|
4.53 km/s |
| 114.900° | |
|
Mean motion
|
0° 0m 12.523s / day |
| Inclination | 17.140° |
| 97.213° | |
| 1934-11-30 (JD 2427771) | |
| 272.579° | |
| Known satellites | 0 (1 suspected) |
| Neptune MOID | 12.040 AU (1.8012 Tm) |
| Physical characteristics | |
|
Mean diameter
|
654+154 −102 km 668+154 −86 km |
|
Mean density
|
0.992+0.086 −0.015 g/cm3 |
| 6.343572±0.000006 h | |
| 0.127+0.04 −0.042 |
|
| IR (moderately red) B−V=0.88±0.02 V−R=0.62±0.01 V−I=1.24±0.01 |
|
| 20.3 (opposition) | |
| 3.79 3.83 (V-band) |
|
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20000 Varuna is a large, icy world found far beyond Neptune in our Solar System. It's part of a region called the Kuiper belt, which is like a giant donut-shaped ring of small, icy objects. Varuna was discovered in November 2000 by an American astronomer named Robert McMillan. This distant object is named after Varuna, an ancient god from Hinduism who ruled over the sky and oceans.
Varuna spins very quickly, which has made it stretch out into an oval shape, like a squashed football. Its surface looks a bit reddish because of special organic compounds that have been changed by sunlight. Scientists also found water ice on Varuna. They think past crashes might have exposed this ice and also made Varuna spin so fast. Even though no moons have been seen directly around Varuna, some changes in its brightness suggest it might have a small, close-orbiting satellite.
Contents
Varuna: A Distant World in Our Solar System
Discovering Varuna
How Varuna Was Found
Varuna was found by astronomer Robert McMillan on November 28, 2000. He used a special telescope called the Spacewatch 0.9-meter telescope. This telescope is located at the Kitt Peak National Observatory in Arizona, USA. McMillan was looking for new objects in space. He noticed Varuna moving slowly against the background stars by comparing different images.
After McMillan's discovery, other astronomers, like Jeffrey Larsen, made more observations. These extra observations helped confirm that Varuna was a new object. On December 1, 2000, the discovery of Varuna was officially announced. It was first called 2000 WR106. This name tells us it was found in the second half of November 2000.
Scientists later found older pictures of Varuna, some from as far back as 1954. These older images are called "precovery images." They helped astronomers figure out Varuna's path around the Sun more accurately. In January 2001, Varuna was given the official number 20000. This number was chosen to show how large Varuna was thought to be at the time. It also honored the 200th anniversary of the discovery of Ceres, another large space object.
Naming This Icy World
Varuna is named after a powerful Hindu god called Varuna. This name was suggested by an Indian choreographer, Mrinalini Sarabhai. The International Astronomical Union (IAU) approved the name in March 2001. In ancient Hindu stories, Varuna is one of the oldest gods. He is known for creating and ruling over the waters of the sky and the ocean. He is seen as a king of gods and humans, with endless knowledge.
Planetary symbols, like the ones for Earth or Mars, are not often used in astronomy anymore. So, Varuna doesn't have an official astronomical symbol. However, some people have suggested symbols for it. One symbol, designed by Denis Moskowitz, looks like the Devanagari letter 'va' and a snake-lasso. Another symbol sometimes seen is a variation of the symbol for Neptune, because Varuna is similar to Neptune in Hindu mythology.
Varuna's Journey Around the Sun
Varuna's Orbit and Classification
Varuna travels around the Sun at an average distance of about 42.7 AU. One AU is the distance from Earth to the Sun. So, Varuna is about 42.7 times farther from the Sun than Earth is! It takes Varuna about 279 Earth years to complete one full trip around the Sun. Imagine how many birthdays that is!
Varuna's path around the Sun is almost a perfect circle. This means its distance from the Sun doesn't change much. At its closest point (called perihelion), it's about 40.3 AU from the Sun. At its farthest point (called aphelion), it's about 45.1 AU away. Varuna passed its closest point to the Sun in 1928. It is currently moving away from the Sun and will reach its farthest point around 2071.
Because of its nearly circular orbit between 40 and 50 AU, Varuna is called a classical Kuiper belt object. These objects are also sometimes called "cubewanos." Varuna is not directly affected by Neptune's gravity in a special way, unlike some other objects in the Kuiper Belt. Varuna is considered a "dynamically hot" classical KBO because its orbit is tilted more than 4 degrees compared to the main plane of the Solar System.
Varuna's Spin and Shape
How Varuna Rotates
Varuna spins very quickly! It completes one full rotation in about 6.34 hours. Scientists figured this out by watching how its brightness changed over time. This change in brightness is called a "light curve." When Varuna spins, different parts of its surface reflect sunlight differently, causing its brightness to vary.
Early observations in 2001 showed that Varuna's brightness changed a lot. This suggested it might have an unusual shape. If Varuna were perfectly round, its rapid spin would cause it to break apart unless it was super dense. Instead, scientists believe Varuna is stretched out, like an ellipsoid. This elongated shape explains the changes in brightness as it spins.
Scientists have also noticed that the way Varuna's brightness changes has increased over the years. This is due to its oval shape, its rotation, and how we view it from Earth. Models suggest that Varuna is currently seen almost "edge-on," meaning its equator is nearly facing Earth.
Scientists think Varuna's fast spin might be due to powerful collisions that happened long ago. These crashes could have sped up its rotation when the Solar System was forming. Even though collisions are rare now, they were more common in the early days of our Solar System.
Varuna's Unique Shape
Because Varuna spins so fast, it isn't perfectly round. Instead, it's stretched into a shape called a "triaxial ellipsoid." This means it has three different lengths for its axes, like a football that's been squashed a bit. Scientists describe its shape as a Jacobi ellipsoid. This means its longest side is about 1.5 to 1.6 times longer than its middle side.
Scientists have used different ways to estimate Varuna's size. These methods include measuring the heat it gives off and watching it pass in front of distant stars. These measurements have given different sizes, ranging from about 500 to 1000 kilometers (310 to 620 miles) across.
For example, in 2010, Varuna passed in front of a star, blocking its light for a short time. This event, called an occultation, showed that Varuna's longest side is about 1003 kilometers (623 miles) long. Later occultations in 2013 and 2014 suggested an average diameter of about 670 to 686 kilometers (416 to 426 miles).
Is Varuna a Dwarf Planet?
Some astronomers once thought Varuna might be a dwarf planet. For an object to be a dwarf planet, it needs to be massive enough for its own gravity to pull it into a round shape. This is called being in "hydrostatic equilibrium." However, calculations suggest Varuna has a very low density, almost like water. This low density means it might not be fully solid inside. It could be a bit porous, like a sponge. If it's not fully solid and round due to its own gravity, then it wouldn't be classified as a dwarf planet.
What Varuna is Made Of
Looking at Varuna's Surface
Scientists study the light reflected from Varuna to learn about its surface. This is called looking at its spectrum. Observations show that Varuna's surface is moderately red. This reddish color comes from organic compounds that have been changed by sunlight and cosmic rays. These changed compounds are called tholins.
Varuna's spectrum also shows signs of water ice on its surface. This ice might have been exposed by past collisions. Some studies also suggest the presence of other icy materials like methane, ethane, and ethylene. Varuna isn't massive enough to hold onto light gases like methane for billions of years. So, the methane might have been put there by a powerful impact.
How Bright is Varuna?
Varuna is quite dim when seen from Earth. Its brightness, called apparent magnitude, changes from 19.5 to 20. The smaller the number, the brighter the object. For comparison, the brightest stars are magnitude 0 or 1. So, Varuna is very faint!
Scientists also measure its absolute magnitude, which is its brightness if it were at a standard distance. Varuna's absolute magnitude is about 3.76. This makes it one of the twenty brightest objects in the Kuiper Belt.
Varuna's surface is relatively dark. It has a geometric albedo of about 0.127. Albedo tells us how much light an object reflects. An albedo of 0 means it reflects no light (perfectly black), and 1 means it reflects all light (perfectly white). So, Varuna reflects about 12.7% of the sunlight that hits it. This is similar to the dwarf planet candidate Quaoar.
Inside Varuna
Scientists believe Varuna has a bulk density of about 0.992 grams per cubic centimeter. This is slightly less than the density of water. This low density suggests that Varuna's inside might be quite porous. It could be made of a mix of water ice and rock, with many empty spaces.
This porous structure might be due to fractures from past collisions. These collisions could also be why Varuna spins so fast. Other objects, like Saturn's moons Tethys and Iapetus, also have low densities and porous interiors. Scientists think that mid-sized objects like Varuna might not have fully melted and settled into a dense core. Their rocky parts might not have gotten hot enough to fill all the empty spaces inside.
A Possible Moon for Varuna?
In 2019, scientists studying Varuna's light curve noticed subtle changes. These changes suggest that Varuna might have a small moon orbiting it very closely. By analyzing the variations in brightness, they estimated that this possible moon orbits Varuna every 11.98 hours.
If this moon exists, it might be orbiting Varuna at a distance of about 1300 to 2000 kilometers (800 to 1200 miles). This is just outside Varuna's Roche limit, which is the closest a moon can orbit without being torn apart by gravity. It's currently impossible to see this moon directly with telescopes like the Hubble Space Telescope because it's too close to Varuna. However, since Varuna's equator is facing Earth, future mutual events (where the moon passes in front of or behind Varuna) might be possible.
Visiting Varuna
Scientists have thought about sending a spacecraft to Varuna. A mission to fly by Varuna could take just over 12 years. This would involve using Jupiter's gravity to speed up the spacecraft, a technique called a "gravity assist." Such a mission could be launched in 2035 or 2038.
Other paths have also been considered. For example, a trajectory using gravity assists from Jupiter and Uranus could take about 13 years, with launch dates in 2034 or 2037. Another option, using gravity assists from Saturn and Uranus, could take under 18 years, with a possible launch in 2029. No matter the path, a spacecraft would arrive at Varuna before 2050, when Varuna would be about 45 AU from the Sun.
See also
In Spanish: (20000) Varuna para niños
