Thursday, May 30, 2013

1998 QE2

During the past weeks we have heard about asteroid 1998 QE2 and how it has got closer than any other asteroid to Earth.  Whether or not it poses any dangers to us or not (well, it does not). In fact, the closest approach of this asteroid to Earth occurs tomorrow, May 31, 4:59 pm Eastern Time, "when the asteroid will get no closer than about 3.6 million miles (5.8 million kilometers), or about 15 times the distance between Earth and the moon". As eyes were on this asteroid to capture this approach, NASA scientists discovered that QE2 has its own moon!   Radar data of NASA's Goldstone Deep Space antenna in California were used for this finding.  Images were taken from "3.75 million miles (6 million kilometers) from Earth, which is 15.6 lunar distances." To learn more read here.

Yet, I wonder, where is my moon?  I mean Vesta's moon?




Reference:

http://www.nasa.gov/mission_pages/asteroids/news/asteroid20130530.html


Posted by Nargess at 5:20 PM
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7 comments:

  1. radiusMay 31, 2013 at 3:04 AM

    Hi Nargess, When I red the title of your post I intuitively thought its about the 1998 cruise of the Queen Elizabeth II. I hope that the path of the asteroid 1998 QE2 is more predictable than the route of her majesties ship QE2.
    regards
    Michael

    PS: And I hope that today, at 4:59 pm Eastern Time, you can give an "All Clear" about the safe encounter of the asteroid with earth.

    ReplyDelete
  2. NargessMay 31, 2013 at 10:22 AM

    Thanks for the information, I looked up QE2 ship. It is fascinating.

    ReplyDelete
  3. radiusJune 2, 2013 at 5:26 AM

    Hi Nargess, I have to admit that I learned something new here (or say, I had to correct a wrong idea of mine): That only planets can have their own moon, meaning having a satellite bound to them by gravitational force. I never thought a small object such as an asteroid with 2.7 km diameter generates sufficient gravitational force to keep another object (here with 600 m diameter) bound to it. But the radar video images of the website leave no doubt that it the asteroid 1998QE2 and its satellite are indeed bound to each other and orbit around each other.
    thanks for sharing, Michael

    ReplyDelete
  4. radiusJune 2, 2013 at 9:26 AM

    Hi Nargess, the moon accompanying this asteroid has another weird feature: Why do you think it appears so bright as compared to the asteroid ? If both simply reflect the sun light (as all planets and comets in the solar system do), the moon cannot be brighter than the big asteroid next to it ?
    I guess somebody is sitting there, and holding up a lighter or a torch or an iPAD display.
    Maybe you have an alternative and more scientifically justified explanation.
    regards, Michael

    ReplyDelete
  5. NargessJune 2, 2013 at 5:32 PM

    Dear Michael,

    Thanks for your interest and comments. It is not uncommon for asteroids, minor planets, to have moons. So far we know of over 200 objects in the solar system with companions (e.g. 243 Ida, 5 Eugenia, 762 Pulcova, 90 Antiope, 87 Sylvia, etc).

    You raise a good point about the brightness level of QE2 and its moon. In reality you expect the primary body be brighter than its secondary object orbiting it. The reason in these images you see the moon brighter than the asteroid is mainly because you are not looking at actual images of these bodies rather radar measurements/reflections sent to and from these objects. These images are a function of distances and velocities of these objects relative to the source of the radar waves sent to them. Radar waves also work like sound waves and are subject to Doppler shifts. This post and a link within it provides more detail (3rd paragraph):

    http://www.slate.com/blogs/bad_astronomy/2013/05/31/asteroid_1998_qe2_moon_discovered_using_radar.html

    Another reason a body may seem brighter than expected even when looking at actual images is also the difference between concepts of apparent magnitude vs. absolute magnitude. In other words, the brightness levels of objects varies depending on whether magnitudes are calculated/observed relative to the Sun, relative to an observer on Earth, relative to a camera on a spacecraft making the observation, or relative to the brightest star Vega, etc.

    I hope this helps.

    p.s. Holding a flashlight/lighter is a good way to think about radar measurements.

    ReplyDelete
  6. radiusJune 2, 2013 at 6:05 PM

    Hi Nargess, thanks a lot for the information. I think I have to revise my understanding about what a moon is: On every pair of objects which are bound to each other by gravitational force and kept on a constant distance by orbiting around each other, the smaller of the two can be considered to be a moon. But than, I assume, the force that keeps the two together might also be quite small, and maybe a collision with a third object might could be sufficient to separate the pair (in your case the asteroid and its moon). I have to calculate how strong the gravitational force between the two could be.
    And about the brightness: Yes, you are right, I forgot that these are radar images, and therein brightness is no direct measure of the size (like on a stealth airplane).

    best regards, Michael

    ReplyDelete
  7. NargessJune 2, 2013 at 6:34 PM

    Hi Michael,

    The definition of the moon I am familiar with is that the secondary object (moon) should reside in the primary object's Hill Sphere region, and obey Newton's and Kepler's laws of gravity and motion with respect to its primary. Therefore, a moon's orbit in general is elliptical and the distances between a primary and its secondary object, moon, does not remain constant as the moon travels along its orbit. Our Moon's orbit is close to a circle with a 0.05 eccentricity, while Jupiter's moons have varying eccentricities as high as 0.6: http://en.wikipedia.org/wiki/Moons_of_Jupiter

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