Frequently Asked Questions About Quaoar


What is Quaoar?

Quaoar is a newly discovered Kuiper Belt object, found in June 2002 by Chad Trujillo and Mike Brown at Caltech in Pasadena. It's the largest Kuiper Belt object currently known, half the diameter of Pluto (about 1/8 the volume), and 1.6 billion kilometers (1 billion miles) further away than Pluto.

How big is Quaoar?

Quaoar is about 1250 km in diameter, roughly the size of Pluto's moon Charon. Nothing larger has been found in our solar system since Pluto was discovered in 1930 (and Pluto's moon Charon in 1978). It's huge, in fact, if you took the 50,000 numbered asteroids and put them together, it would be about the same volume as Quaoar.

Here's a picture of Quaoar compared to some other Solar System objects.

Quaoar vs. the Solar System
(NASA and A. Feild (STSci)

Is Quaoar a Planet?

We don't think so. It's about half the size of Pluto and further away, but there are other big objects out there, too. Varuna (900 km in diameter) and 2002 AW197 (also 900 km in diameter) are two of the biggest Kuiper Belt Objects, and they are not considered "planets" either. There are about 600 known Kuiper Belt Objects, most of which are only about 100 km in diameter, and all of which were discovered since 1992 by different scientists who have been looking for them. It's similar to the asteroid belt, but beyond Neptune and contains maybe 100 times more material. You can read more about the Kuiper Belt at the Kuiper Belt Homepage. Note that the Kuiper Belt is also called the Edgeworth-Kuiper Belt and the trans-Neptunian Belt. We think we should be able to find 5 - 10 more of these really big Kuiper Belt Objects over the next couple of years, including perhaps a couple "super-Plutos".

How was Quaoar found?

First of all, we are looking for objects like Quaoar because we think there may be a lot of objects like it that are undiscovered, and maybe even objects bigger than Pluto. We spent about 7 months looking for it with a semi-automated telescope, the Oschin Telescope at Palomar, California. It has a mirror diameter of 48 inches (1.2 meters), which is large compared to amateur telescopes (typically ranging from 0.1 - 0.3 meters in diameter), but small compared to most professional telescopes (1 - 10 meters in diameter). Although the mirror isn't very big, the Oschin Telescope has a huge field of view for its size, about 3 square degrees. That's about the same amount of sky area as 12 moons in each picture.

Here's the discovery images. We took three pictures of the same patch of sky with 90 minutes between them. These pictures are about 150th of the entire field we get with the telescope. In a single night, we cover about 1700 times the area you see below. Click for enlargement:

Quaoar Discovery Images

You can download the raw data here.

What is that other, faint object in the image?

There's lots of little specks in the images, most of them are "static" caused by cosmic rays --- similar to the static on your t.v. Sometimes they line up and look a lot like a moving object. So basically, we ignore anything that is only one or two pixels in size --- it really has to look a lot like a star, being several pixels across and "round" looking. Also, it has to move in a straight line and be present on all the images. You can probably find a lot of these things in the discovery images that it don't fit all the criteria of a real object.

Also, it's true that we may miss some very faint objects. But we are interested in finding the brightest ones, so in the interest in saving time, because there are only a couple of us working on this project and there is a lot of data, some of the faintest objects may be real, and we may not recognize them in the images. But we consider that "acceptable loss" because we are looking for the biggest, brightest things anyway. People in the future will find the smaller, fainter things.

How far away is Quaoar?

Quaoar is at about 42 AU away from us, more distant than Pluto and Neptune, which are both at about 30 AU. 1 AU is an "Astronomical Unit" and is equal to the distance between the Earth and the Sun, about 150 million kilometers. So Quaoar is about 6 billion kilometers from us. At walking speed, it would take you about 100,000 years to get there. Going at the speed the Space Shuttle orbits the earth, it would take 25 years to get there. It takes light 5 hours to get there from the sun.

Quaoar is in a nearly circular orbit. Its eccentricity (a measure of the ellipticity of a circle) is less than 0.04, meaning that its distance from the sun only changes by about 8% over the course of a Quaoar year (which is 285 Earth years). This is very different from Pluto, which has an eccentricity about 6 times larger. You can see its orbit below. Because this object is so bright, within a month of discovery we were able to trace Quaoar's position back two decades in survey data. Quaoar's orbit is also inclined to the ecliptic (the plane of the solar system), by about 8 degrees.

This process is often called "precovery". Click on that link, it's cool.

Quaoar's orbit (red) compared to the planets (black). The Gas Giant planets (Jupiter, Saturn, Uranus and Neptune) and Pluto are labeled with the first letter of their name. Click for a bigger mpeg version.

Quaoar's Orbit

Are Quaoar and Pluto going to crash into each other?

No, it kind of looks like it from the picture above of the orbits, but they don't collide, Quaoar's orbit is tilted with respect to the other planets by about 8 degrees. Pluto is tilted by about 20 degrees, so although it looks like they might hit each other from the "top view", a "side view" would show that their orbits don't intersect.

How do we know how big Quaoar is?

We measured the size of Quaoar in two ways:

(1) Optical measurements using the Hubble Space Telescope. Using a normal ground based telescope, you can't see Quaoar's size directly. You can tell it's there, but it's just a pinpoint of light just like any other star. But, the Hubble Space Telescope (HST) has much better "angular resolution" (it can see details a lot better) than a normal telescope because it is outside the Earth's atmosphere. By very carefully measuring Quaoars size about 10 times over the course of an hour and comparing them to a nearby star, we can see directly that Quaoar is 1250 km in diameter.

You can see the HST images here. Note that the vertical elongation is due to object motion during the exposure ("blurring"), and not the size of the object. Also, there is a paper about this technique here.

(2) Thermal measurements. Using the IRAM telescope in Spain, we measured the heat coming from Quoar. Optical wavelength light (i.e. what your eye sees and what a "normal" telescope measures) only tells you about the amount of sunlight that is reflected from Quaoar back to Earth. So, a small white object could reflect the same amount of light as a large dark object. However, a dark object absorbs much more light than a white object, so it will be hotter. By measuring the heat (1.2 millimeter wavelength "light") coming from Quaoar and comparing it with the optical reflected light, we know that Quaoar has a diameter of 1250 km.

Where did the name come from?

The Tongva people (sometimes called the San Gabrielino Native Americans) inhabited the Los Angeles area before the arrival of the Spanish and other European people. The name "Quaoar" (pronounced kwah-o-wahr) comes from their creation mythology. In the words of Mark Acuña, Tongva scholar, dancer and tribal elder:

"'Quaoar' the great force of creation sings and dances the high ones (Deities) into existence. While Quaoar has no form or gender he is usually referred to with the male pronoun. He dances and sings first 'Weywot' who becomes Sky Father; they sing and dance 'Chehooit' Earth Mother into existence. The trio sing 'Tamit' Grandfather Sun to life. As each divine one joins the singing and dancing, the song becomes more complex and the dance more complicated. In turn 'Moar', Grandmother Moon (a very complex deity), 'Pamit' the Goddess of the sea, 'Manit', the Lord of dreams and visions, 'Manisar' the bringer of food and harvests, 'Tukupar Itar' Sky Coyote (who is also our major hero), 'Tolmalok', the Goddess of Shishongna (the underworld) join in the singing, dancing and creating. And finally the great seven giants who hold up the worlds are created. The High Ones in turn are aided by 'Eagle, Duck, Bear, and Frog' in a grand earth diving story. Frog brings up soil out of the deep dark sea, and the four animals dance it flat and wide. The 'Gods and Goddesses' then furnish the world 'Tovangar' with hills, mountains, trees, rivers, etc. 'Tobohar' (first man) and 'Pahavit' (first woman) are also part of this great 'Creation song and dance cycle'."

You can find out more about the Tongva at the Tongva website.

The IAU has voted and approved the name Quaoar, which is now its official name.

What is Quaoar made of?

We don't know exactly. We suspect that most Kuiper Belt Objects are made of equal portions of rock and ices. There are many chemicals which are normally liquids or gas on Earth that would be different types of ice on Quaoar, including water, methane ice (natural gas ice), methanol ice (alcohol ice), carbon dioxide ice (dry ice), carbon monoxide ice (very gross) and others. We know that there is water ice on Quaoar from measurements made at the Keck Telescope.

Are there more big Kuiper Belt Object like Quaoar that we haven't seen?

It is very likely that there are more big Kuiper Belt Objects like Quaoar. We looked at only 5% of the entire sky before finding Quaoar. So there could be 20 Quaoars out there and we wouldn't have seen them yet. It is also likely that a few Plutos are out there waiting to be discovered. We have so far looked mostly in the plane of the solar system, where objects are most likely to be. It's likely that our discovery rates will go down as we get further and further from the solar system plane (the ecliptic) but we still expect to find maybe 10 more objects, given current models of the Kuiper Belt thickness.

Where is it?

Here's the ephemeris, in J2000 coords. Times are in UT, right ascension in hours, declination in degrees. It has a red magnitude of 18.6 or so right now. Or get it from HORIZONs, which will give you the position of any solar system body for any time you want.

2003-Mar-12 08:00 16 47 53.48 -15 14 22.5
2003-Mar-19 08:00 16 47 52.25 -15 13 04.1
2003-Mar-26 08:00 16 47 46.40 -15 11 39.4
2003-Apr-02 08:00 16 47 36.06 -15 10 09.4
2003-Apr-09 08:00 16 47 21.45 -15 08 35.6
2003-Apr-16 08:00 16 47 02.92 -15 06 59.6
2003-Apr-23 08:00 16 46 40.83 -15 05 22.7
2003-Apr-30 08:00 16 46 15.57 -15 03 46.4
2003-May-07 08:00 16 45 47.61 -15 02 12.2
2003-May-14 08:00 16 45 17.49 -15 00 41.5
2003-May-21 08:00 16 44 45.73 -14 59 15.8
2003-May-28 08:00 16 44 12.89 -14 57 56.2
2003-Jun-04 08:00 16 43 39.53 -14 56 44.0
2003-Jun-11 08:00 16 43 06.27 -14 55 40.5
2003-Jun-18 08:00 16 42 33.69 -14 54 46.6
2003-Jun-25 08:00 16 42 02.30 -14 54 03.1
2003-Jul-02 08:00 16 41 32.66 -14 53 30.7
2003-Jul-09 08:00 16 41 05.30 -14 53 10.2
2003-Jul-16 08:00 16 40 40.69 -14 53 01.8
2003-Jul-23 08:00 16 40 19.23 -14 53 05.6
2003-Jul-30 08:00 16 40 01.31 -14 53 21.8
2003-Aug-06 08:00 16 39 47.27 -14 53 50.3

Orbital Elements

Here's the orbital elements, as computed by the method of Bernstein & Khushalani (2000):

# Barycentric osculating elements in ICRS at epoch 2445471.8:
a 43.373493 +/- 0.009720 AU
e 0.037457 +/- 0.000055
i 7.992 +/- 0.000 deg
Node 188.923 +/- 0.001 deg
Arg of Peri 156.292 +/- 0.242 deg
Time of Peri 2478635.182 +/- 76.022 JD

What was the time, date and place of discovery?

The first discovery image was taken at 2002 June 04 05:41:40 (Universal Time = Greenwich, England) from the Palomar Observatory 48-inch Oschin telescope. I identified Quaoar in the image at 2002 Jun 05 10:48:08 (Pacific Daylight Time).

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Chad Trujillo
email: trujillo at gemini dot edu