Asteroid 101955 1999 RQ36 and friends

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Since the recent reanalysis of 101955 (1999 RQ36) has made headlines, I will start a discussion on it. I'll dig up earlier posts from the first long term risk estimate from about a year ago and append it to this thread.

Here are the top 6 risk asteroid impacts as of Aug 1 2010:

Object............. VI years ...# of VI's... Impact odds...Vinf...H....size(km)...PS cumulative..PS max..TS
101955 1999 RQ36 .............2169-2199... 8... ..7.1e-04 ...6.36 ...20.7 ...0.560... -1.12 ...-1.52 ...n/a
(No Perm #) 2007 VK184 ......2048-2057 ...4 ...3.4e-04... 15.63 ...22.0... 0.130 ...-1.82... -1.83 ...1
99942 Apophis (2004 MN4) ...2036-2103.... 6 ....7.4e-06 ...5.87... 19.7 ...0.270 ...-2.97 ...-3.08... 0
(No Perm #) 1994 WR12 .....2054-2106... 121... 9.1e-05 ...9.84 ...22.4 ...0.110... -2.99 ...-3.92... 0
(No Perm #)1979 XB ..........2056-2086..... 2 ....3.0e-07... 24.59 ...18.5... 0.687... -3.05... -3.09 ...0
(No Perm #) 2010 AR85 ......2015-2106 ...35 ...1.9e-08 ...32.84 ...17.4 ...1.100... -3.11... -3.37 ...0

For those new to the asteroid game, let me explain the data listed (this is all from the JPL Sentry system, more on that later; the other source is NEODyS, and for well studied objects, the numbers are very close)

Object description

Any new asteroid is given a discovery designation (I'll use Apophis as an example since it has all 3) such as 2004 MN4
This consists of the year of discovery (2004) a letter for the half month of discovery (M) and a letter and numbers for objects discovered during the half month (N4).

For objects well observed over multiple oppositions, a permanent number (like 99942) is assigned.

After that suggested names (such as Apophis) may be submitted to the IAU.

Virtual Impactors:

For each object, the observations (with their error bars) are used to calculate orbits that match the observations. In the beginning there are thousands of orbits that can fit the observations. As more data comes in, the number (or really the distribution) of the possible orbits is reduced. Orbits that could possibly impact earth are called virtual impactors. The years during which those impacts can occur is the next entry, then the number of VI's.

Impact odds:

Next is the cumulative possibility of impact. For example, the highest risk, for 1999 RQ36 is

Impact Probability: 7.1e-04
0.071000000% chance of Earth impact
1 in 1,410 chance
99.92900000% chance the asteroid will miss the Earth


This is the approach speed o the asteroid to earth before earth's gravity affects it. The earth provides a constant acceleration of 11.2 km/sec, so this is added to the Vinf according to the formula Vimpact=SQRT(Vinf^2 + 11.2^2).

So the lowest possible impact velocity is 11.2 km/sec (for an impossible object with zero starting speed relative to earth), for Apophis (5.87 Vinf) the impact velocity is 12.6 km/s, for 2010 AR85 impact speed is 34.7 km/s, and the fastest possible for an object orbiting the sun is ~ 72 km/sec for an object orbiting the sun retrograde such as the parent comet of the Leonids or Halley's comet (Orionid and eta Aquariid meteor showers).

H and diameter are related; H is the absolute magnitude (standard distance and illumination) and the diameter is an estimate in most cases based on assumptions of the albedo (reflectivity) of the object. In some cases the size is firmed up by direct visual or radar observations, but in most cases it's a best guess.

PS is the Paletmo Scale, cumulative is all VI's, max is the highest likelyhood individual impact.

TS is the Torino Scale, only defined for impacts within the next century

Palermo Scale:

Torino Scale:


I posted on this several days ago in the other asteroid thread (I was too lazy to start a new thread): It seems the arXiv paper published in April is finally getting some attention.

An interesting paper on hazardous asteroid 1999 RQ36 , which has about a 1 in 1500 chance of hitting the earth, most likely in 2182. It is perhaps the most hazardous asteroid known. Observations in 2011 and 2018 will help greatly to refine the future orbit further and to help paramaterize the impact of the Yarkowsky effect. If these future observations show that a collision is likely, according to the paper, a deflection mission would need to be launched in 2060, when 1999 RQ36 passes through a 'keyhole'. If we wait til after 2060, then it will be very difficult to deflect. An impact from this 560m diameter object would have the energy of 2700 MT.
pdf of full paper:

radar image:


Yes, your and EarthlingX's post inspired me to create this dedicated thread. His from SB&T is copied below with the links.
I'll add other links soon.

by EarthlingX » Tue Jul 27, 2010 11:32 am

More about (101955) 1999 RQ36 : : Potentially hazardous asteroid might collide with the Earth in 2182

"The potentially hazardous asteroid, (101955) 1999 RQ36, has a one-in-a-thousand chance of impacting the Earth, and more than half of this probability indicates that this could happen in the year 2182, based on a global study in which Spanish researchers have been involved. Knowing this fact may help design in advance mechanisms aimed at deviating the asteroid's path.

"The total impact probability of asteroid '(101955) 1999 RQ36' can be estimated in 0.00092 -approximately one-in-a-thousand chance-, but what is most surprising is that over half of this chance (0.00054) corresponds to 2182," explains to SINC María Eugenia Sansaturio, co-author of the study and researcher of Universidad de Valladolid (UVA). The research also involved scientists from the University of Pisa (Italy), the Jet Propulsion Laboratory (USA) and INAF-IASF-Rome (Italy).

Scientists have estimated and monitored the potential impacts for this asteroid through 2200 by means of two mathematical models (Monte Carlo Method and line of variations sampling). Thus, the so called Virtual Impactors (VIs) have been searched. VIs are sets of statistical uncertainty leading to collisions with the Earth on different dates of the XXII century. Two VIs appear in 2182 with more than half the chance of impact."


Old posts (to see if there are any changes) From this thread:

From Feb 13
"101955 1999 RQ36 has a higher cumulative risk of -1.12 for it's 8 impacts from 2169-2199, the highest event PS is -1.52)"

by MeteorWayne » Wed Feb 17, 2010 7:53 pm

There's an even higher risk of impact asteroid than this, 101955 1999 RQ36 . It has a 1 in 1410 chance of impact cumulatively among 8 virtual impactors between 2169 and 2199, with the highest of them (~ 1 in 3570) in 2182. It hasn't been observed since 2006.

Preprint Abstract:

These two asteroids were selected for special examination beyond the 100 year time period that Sentry normally looks at due to the potentil for high risk.

From May 18:

The highest risk asteroid is 101955 (1999 RQ36) with a 1 in 3750 chance of impact in the year 2182...that's 172 years from now.


Yarkovsky Effect:

"The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum. It is usually considered in relation to meteoroids or small asteroids (about 10 cm to 10 km in diameter), as its influence is most significant for these bodies....

The Yarkovsky effect is a consequence of the time needed for the surface to warm up or cool down. In general there are two components to the effect:

Diurnal effect: On a rotating body (e.g. an asteroid) illuminated by the Sun, as on the Earth, the surface is warmer in the afternoon and early night, than in the morning and late night. The result is that more heat is radiated on the "dusk" side than the "dawn" side, leading to a net radiation pressure thrust in the opposite "dawn" direction. For prograde rotators, this is in the direction of motion on their orbit, and causes their semi-major axis to steadily increase, spiraling away from the Sun. Retrograde rotators spiral inward. The diurnal effect is the dominant component for larger bodies greater than about 100 m diameter.
Seasonal effect: This is easiest to understand for the idealised case of a non-rotating body orbiting the Sun, for which each "year" consists of exactly one "day". As it travels around its orbit, the "dusk" hemisphere which has been heated over a long preceding time period is invariably in the direction of orbital motion. The excess of thermal radiation in this direction causes a "braking" force which always causes spiraling inward toward the Sun. In practice, for rotating bodies, this seasonal effect increases along with the axial tilt. It dominates only if the diurnal effect is small enough. This may occur because of very rapid rotation (no time to cool off on the night side, hence an almost uniform longitudinal temperature distribution), small size (the whole body is heated throughout) or an axial tilt close to 90°. The seasonal effect is more important for smaller asteroid fragments (from a few metres up to about 100 m), provided their surfaces are not covered by an insulating regolith layer and they do not have exceedingly slow rotations. "


Nice work MW, thanks :cool:

Some spam from "Asteroid sample return mission proposal" thread :

EarthlingX":2z3ary65 said:
I checked the rock, and here are some facts and aerobics :

from Wiki : (101955) 1999 RQ36
(101955) 1999 RQ36 is the minor planet designation of an Apollo asteroid discovered by LINEAR in 1999. It has a mean diameter of approximately 510 meters, and has been observed extensively with the Arecibo Observatory Planetary Radar and the Goldstone Deep Space Network ([1][2][3], see also radar astronomy).
Separately, RQ36 has been considered multiple times as the target of spacecraft missions, including OSIRIS, due to the low delta-v required to reach it from Earth orbit.

I will, just for fun, try some calculations, please check it :
Volume = (4 x pi x (510 m)^3)/3 = 555 647 209,456 m^3 , or very close mass in water, expressed in t.

If i assume density of 2 kg/l, or 2 t/m^3, it's a bit of orientation, and not too hard calculation ( with not rounded numbers ) :
555 647 209,456 m^3 * 2 t/m^3 = 1 111 294 418,91 t

Now let's get some perspective, like something big :

Wiki : Bulk carrier
A bulk carrier, bulk freighter, or bulker is a merchant ship specially designed to transport unpackaged bulk cargo, such as grains, coal, ore, and cement in its cargo holds. Since the first specialized bulk carrier was built in 1852, economic forces have fueled the development of these ships, causing them to grow in size and sophistication. Today's bulkers are specially designed to maximize capacity, safety, efficiency, and to be able to withstand the rigors of their work.
Today, bulkers make up 40% of the world's merchant fleets and range in size from single-hold mini-bulkers to mammoth ore ships able to carry 365,000 metric tons of deadweight (DWT).

How many of this big ships for one tiny rock ?

1 111 294 418,91 t / 365 000 = 3044,642 ships .

If, for the sake of simplicity i assume 1 week travel time, including loading and unloading, might be possible with bulk carriers, don't know, and
100 ships = 30,44642 weeks, and using 4,5 as weeks/month approximately 6 - 7 months.
10 ships = 304,4642 weeks, 67,6587 months, 5,638225 years ..

Adjust accordingly.


Doesn't make too much of a difference in your calculations, but the latest data (used in the paper that started this kerfluffel), are diameter 560 meters, and bulk density 1500 kg/m^3.


what would the view be like from this asteriod. Can venus or mars get hit? Better yet I'm sure, a asteriod asteriod impact is far more likely. And much more useful. What the mass of the asteriod belt is about the size of a small planet.
So an asteriod asteriod impact should be something like a million times more likly. Varous Ice particles would fly out and
stuff. Some people here have questioned the notion of updating probalities. They are real. When they say the odds are
1/1000 they mean it. Wake up. I don't want to get hit by an asteriod. So what if we do pick one up, heading for us. we send a robot out there to get rid of it. I would put a solar sail on it. ofcourse there is no reason why the asteriod
could not be studied up close at the same time as it is being deflected. If it is a class M asteriod, that would be interesting. Any clue yet as to where carbonasous chandrites come from. I got one in my house but don't where it comes from. The best thing to do is make shure you don't break the thing apart. We still got a blind spot in the southern hemisphere where we can get hit. we can deflect it if we wish. The sooner we detect it, the less energy it will
take. Some people forget that we could get hit by two asteriods at the same time. It might be eisier to deflect the asteriod into the center of the pacific or atlantic. I know some people don't like the tsuanami, but what the heck. Boston
is a buatiful city and would be spared. Load my star bourd engine will you a little. Ok just put something in the printer
and hit Menu. You use some of the buttons on the left side of the printer. Tell me what happens.


A rather hard to understand post, but wanted to correct one thing. The combined material in the asteroid belt would create an object smaller than our moon.
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