Starship Asterisk*

http://astrobob.areavoices.com/?blog=78068 wrote:
1998 QE2 asteroid flyby an opportunity for pros and amateurs alike
by Astrobob, May 18, 2013

[b][color=#0000FF]Many separate telescopic images were combined to create this animation of asteroid 1998 QE2 moving through a star field this past week. Credit: Ernesto Guido and Nick Howes[/color][/b]

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[b][color=#0000FF][size=150]Mass of 1998 QE2 ~[/size] 64,000 QE2's [size=125]Speed of 1998 QE2 ~[/size] 640 QE2's[/color][/b]

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<<An asteroid it would take an hour to walk across will speed past Earth on May 31 and provide radio astronomers a perfect opportunity to nab closeup views of its surface. 1998 QE2, discovered in 1998 by the Massachusetts Institute of Technology Lincoln Near Earth Asteroid Research (LINEAR) program, will miss our planet by a healthy 3.6 million miles or 15 times the distance of the moon. Closest approach occurs at 3:59 p.m. Central time.

The asteroid’s large size combined with its relatively close approach makes it a great target for both the 230-foot Goldstone radio dish and 1,000-foot Arecibo dish in Puerto Rico. Lance Benner, the principal investigator for the Goldstone radar observations from NASA’s Jet Propulsion Laboratory in Pasadena, Calif., will have all hands on deck for the flyby. By sending bursts of radio waves at 1998 QE2 and measuring the retured radar echoes, Benner expects the dishes to resolve surface features as small as 12 feet across on the 1.7-mile-long asteroid (2.7 km).

Through an ordinary optical telescope, even a large one, 1998 QE2 will appear as a point of light. Radar observations reveal far more including shape, size, rotation and a wide variety of surface features. Goldstone observations are scheduled from May 30 – June 9; those at Arecibo for several days around June 5.

Already optical telescopes in the southern hemisphere have this monster rock in their cross-hairs. By measuring repeating highs and lows in the asteroid’s brightness as it spins on its axis, astronomers can determine its rotation rate. 1998 QE2′s composition is gleaned by how it reflects sunlight. Reflected sunbeams streaming back to Earth carry the imprint of particular minerals that absorb and reflect portions of the sun’s light in unique ways that nail down their identities. “It is tremendously exciting to see detailed images of this asteroid for the first time,” said Benner. “With radar we can transform an object from a point of light into a small world with its own unique set of characteristics. In a real sense, radar imaging of near-Earth asteroids is a fundamental form of exploring a whole class of solar system objects.”

1998 QE2 looks like a point of light in this time exposure taken remotely with a telescope in Australia by the team of Ernesto Guido and Nick Howes. The asteroid is currently very faint and only visible in the southern hemisphere. I’m excited about the asteroid because it will be bright enough to be visible in small telescopes across both northern and southern hemispheres for several nights around the time of closest approach. Between May 30 and June 5 it will shine at 10.5-11.0 magnitude while chugging through the constellations Libra and Ophiuchus, both conveniently placed at nightfall. Its steady movement across the sky – 2/3 of a full moon diameter an hour – will be obvious through the telescope.>>

bystander wrote:
Asteroid 1998 QE2 to Safely Pass Earth Tomorrow
Slate Blogs | Bad Astronomy | 2013 May 30

• It's a cruise ship....what could go wrong

neufer wrote:

bystander wrote:
Asteroid 1998 QE2 to Safely Pass Earth Tomorrow
Slate Blogs | Bad Astronomy | 2013 May 30

• It's a cruise ship....what could go wrong

The radar imagery revealed that 1998 QE2 is a binary asteroid. In the near-Earth population, about 16 percent of asteroids that are about 655 feet (200 meters) or larger are binary or triple systems. Radar images suggest that the main body, or primary, is approximately 1.7 miles (2.7 kilometers) in diameter and has a rotation period of less than four hours. Also revealed in the radar imagery of 1998 QE2 are several dark surface features that suggest large concavities. The preliminary estimate for the size of the asteroid's satellite, or moon, is approximately 2,000 feet (600 meters) wide. The radar collage covers a little bit more than two hours.

Beyond wrote:

neufer wrote:

bystander wrote:
Asteroid 1998 QE2 to Safely Pass Earth Tomorrow
Slate Blogs | Bad Astronomy | 2013 May 30

• It's a cruise ship....what could go wrong

Well... The Titanic and Achille Lauro come to mind.

http://bigbangtheory.wikia.com/wiki/The_21-Second_Excitation wrote:
<<The so-called "submarine controversy" from Raiders of the Lost Ark refers to the scene where Indiana Jones grabs hold to the outside of a Nazi submarine and rides it all the way to their hidden island base. The "controversy" is how Indy knew the sub wouldn't submerge and likely cause him to drown. In novelizations and comic adaptations of the film, The submarine does submerge, but Indy lashes himself to the periscope, which remains above water.>>

http://www.planetary.org/blogs/emily-lakdawalla/2013/05301616-say-hi-to-asteroid-1998qe2.html wrote:
Say "hi!" to asteroid -- actually, asteroids -- (285263) 1998 QE2
Posted By Emily Lakdawalla
2013/05/30 06:51 CDT

<<Here are the first-released radar images of the asteroid [(285263) 1998 QE2], which contain a little surprise: the asteroid has a moon! In fact, it's quite a large moon, maybe 15-25% the size of the main body. I know it doesn't look that big in the images below; I'll explain why in a moment.

[b][color=#0000FF]Animation of 13 images captured by the Goldstone radio telescope on May 30, 2013, as asteroid (285263) 1998 QE2 was only 6 million kilometers from Earth. Its closest approach was yet to come, on May 31 at 20:59 UTC. NASA / JPL / Emily Lakdawalla[/color][/b]

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Of course the first thing I want to do with a set of fifteen images is to animate them. NASA posted their own animation, but I like to process the images a bit first to reduce the distracting effect of the radio speckle (by performing a Gaussian blur) and to try to make the pictures match each other in brightness a little better. That's what I did to produce the animation below. You can see that although the main body has a fairly round shape, it very clearly has some large craters on it.

Okay. So now that I've posted those, how is it possible that the moon visible here as a bright white droplet is a fifth of the size of the asteroid? I'm going to refer you, first, to my explainer on how radar imaging works. A very abbreviated explanation: radar images of asteroids are also called "delay-Doppler" images. The y-axis is "delay" -- how long it took the broadcast radio signal to return to the telescope -- and is directly related to distance to the different parts of the asteroid. The x-axis is "Doppler" -- a measure of how much the radio frequency of the return pulse has been Doppler-shifted, which, in turn, is affected by how fast the thing is rotating. The faster it rotates, the more spread in Doppler.

The delay resolution is 75 meters per pixel. Measure the height of the main asteroid in this image and you'll get about 20 pixels, which is about 1.5 kilometers. Assume the asteroid is roughly spherical, and that translates to a diameter of 3 kilometers. (The NASA release says 2.7 kilometers.) Measure the height of the smaller satellite and you get about 6 pixels, or 450 meters, give or take. (The NASA release says 600 meters. I trust their interpretation of their images more than mine, of course!)

I'm not sure what the Doppler resolution is exactly, but it appears that the main asteroid is rotating relatively quickly (a rotation period of less than four hours, according to the NASA release), while the moon is not rotating nearly as fast. In fact it's very likely the satellite is rotating at exactly the same speed at which it's orbiting the asteroid, maybe a factor of 10 slower than the asteroid's rotation period (according to Alan Harris). That much slower rotation squishes the moon along the Doppler axis, making it appear very skinny compared to the primary. It also concentrates the power of the returned radio signal into those few squished pixels, making it appear much brighter than the primary.

http://en.wikipedia.org/wiki/Pip_%28Great_Expectations%29 wrote:
<<[Prince] Philip Pirrip, called Pip, is the protagonist and narrator in Charles Dickens's novel Great Expectations (1861). Pip narrates his story many years after the events of the novel take place. The novel follows Pip's process from childhood innocence to experience. He's known to himself and to the world as Pip because his "infant tongue could make of both names nothing longer or more explicit than Pip".>>

Stay tuned for more cool radar images. They'll be zapping it with Arecibo, too. I learned this week from Lance Benner's talk to the Society for Astronomical Sciences that by virtue of its much larger diameter, Arecibo is much more sensitive than Goldstone, as you would expect. However, Goldstone is capable of transmitting a radio signal with finer resolution than Arecibo, attaining 3.75 meters' resolution in range. And those tricky, tricky radio scientists can actually take advantage of both capabilities simultaneously: they can perform a bistatic radar observation where they zap it from Goldstone (using Goldstone's finer resolution) and receive the signal at Arecibo (using Arecibo's greater sensitivity) to get images five or 6 times more sensitive than Goldstone can manage alone. I'm not sure if they'll be using that particular trick for QE2, though. This asteroid is not passing as close as some do, so that will affect the maximum resolution they can achieve.>>

mjimih wrote:
can someone direct me to an article that explains why the Earth won't try to steal the little satelite away from the asteroid when it flies by?

geckzilla wrote:What about just changing its orbit rather than stealing it?

geckzilla wrote:
What about just changing its orbit rather than stealing it?

• Maybe 400 km.

http://en.wikipedia.org/wiki/%28285263%29_1998_QE2 wrote:
<<(285263) 1998 QE2 is a near-Earth asteroid 2.75 kilometers in diameter. It was discovered on August 19, 1998, by the Lincoln Near Earth Asteroid Research (LINEAR) program located near Socorro, New Mexico. The surface of 1998 QE2 is covered with a sooty substance, suggesting that this asteroid may have previously been a comet that experienced a close encounter with the Sun. However, the Tisserand parameter with respect to Jupiter (T_J=3.2) does not make it obvious whether 1998 QE2 was ever a comet. The asteroid is optically dark with an albedo of 0.06. As an Amor asteroid, the orbit of 1998 QE2 is entirely beyond Earth's orbit. The Earth minimum orbit intersection distance (E-MOID) with the orbit of the asteroid is 0.035 AU. The asteroid has an orbital period of 3.77 years.>>

http://en.wikipedia.org/wiki/Tisserand_parameter wrote:
<<Tisserand's parameter (or Tisserand's invariant) is a combination of orbital elements used in a restricted three-body problem, named after French astronomer Félix Tisserand. T_J, Tisserand’s parameter with respect to Jupiter as perturbing body, is frequently used to distinguish asteroids (typically ) from Jupiter-family comets (typically ).

For a small body with semimajor axis , eccentricity , and inclination , relative to the orbit of a perturbing larger body with semimajor axis a_P, the parameter is defined as follows:

• 

The quasi-conservation of Tisserand's parameter is a consequence of Tisserand's relation.

Tisserand's parameter is derived from one of the so-called Delaunay standard variables, used to study the perturbed Hamiltonian in a 3-body system. Ignoring higher-order perturbation terms, the following value is conserved:

• 

Consequently, perturbations may lead to the resonance between the orbital inclination and eccentricity, known as Kozai resonance. Near-circular, highly inclined orbits can thus become very eccentric in exchange for lower inclination. For example, such a mechanism can produce sungrazing comets, because a large eccentricity with a constant semimajor axis results in a small perihelion.

• The roughly constant value of the parameter before and after the interaction (encounter) is used to determine whether or not an observed orbiting body is the same as a previously observed in Tisserand's Criterion.
  
  The quasi-conservation of Tisserand's parameter constrains the orbits attainable using gravity assist for outer Solar system exploration.
  
  T_N, Tisserand's parameter with respect to Neptune, has been suggested to distinguish Near Scattered Objects (believed to be affected by Neptune) from Extended Scattered trans-Neptunian objects (e.g. 90377 Sedna).>>

neufer wrote:

mjimih wrote:
can someone direct me to an article that explains why the Earth won't try to steal the little satelite away from the asteroid when it flies by?

The Earth pulls almost equally on QE2 and its satellite.

The L₁ Lagrangian point: is about 800 kilometers above the surface of QE2 such that the satellite would have to orbit at least that high above QE2 for the Earth to have a chance to steal it away.

neufer wrote:

geckzilla wrote:
What about just changing its orbit rather than stealing it?

• Maybe 400 km.

• 1) on average, perpendicular to the satellite velocity (and, hence, ineffective)
  2) of a fleeting duration much shorter than the L₁ satellite period (~4.5 years in this case).

neufer wrote:Upon reconsideration: the tidal effects by the Earth on the satellite are much less than I originally thought.

This is because tidal effects by the Earth are:

• 1) on average, perpendicular to the satellite velocity (and, hence, ineffective)
  2) of a fleeting duration much shorter than the L₁ satellite period (~4.5 years in this case).

Hence, any satellite of an Earth grazing asteroid must be many L₁ distances away to be affected.

mjimih wrote:
So in summation the 1998Qe2 stayed too far away and was going too fast for it's satellite to be stolen. The Earth could change the asteroid and it's satellites' orbits a little bit though.

mjimih wrote:
Is an Earth sized Earth less likely to pull in a killer rock over time as apposed to a Super Earth simply, in this exercise, due to the fact that a large rock would have to get that much closer to it? Would a Super Earth be more vulnerable to snaring a rock directly into it, as apposed to an Earth sized Earth? I suppose much depends on the angle of incidence in which the rock is approaching the planet in the first place too of course.

• 1) It is a large target
  2) It has a strong gravity
  3) It is moving relatively slowly (especially for objects that sneak up on it from behind)

mjimih wrote:
Is Earth possibly intelligent because it is small enough to not be pulling these errant rocks into it "as often" as larger Earths might be able to do? Would a super Earth always be attracting large destructive rocks to it so often or regularly that intelligence would have trouble developing to the math and physics teacher level.

mjimih wrote:
Maybe a super Earth would scour more of it's resident asteroids and comets from it's area sooner and more efficiently, so that after it has done so, it would possibly have more tranquil skies leading to a nice long period of evolution that could lead to scientists who teach math 'n physics, like here.

neufer wrote:

mjimih wrote: So in summation the 1998Qe2 stayed too far away and was going too fast for it's satellite to be stolen. The Earth could change the asteroid and it's satellites' orbits a little bit though.

Yes, and it changes both asteroid & satellite orbits a little bit in the same way.