# Sunshine nudges asteroid into odd orbit

New NASA measurements of the orbit of the half-kilometer asteroid 1999 RQ36 have given space science its most precise measurement of such space rocks' orbit – and revealed a 160km deviation from the orbit predicted by gravity. The drift, which showed up by comparing observations made in 1999, 2005, and September 2011, is due to …

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#### No Reg units?

The other day, I think, we decided on hamsters (~53 hamsters per Watt) as a measurement of power. There must be a work equivalent we could use here. Power and work, I believe, are gaps in the Reg calculator...

#### Re: No Reg units?

Power and work but anyone reading The Reg and posting comments cannot be working (unless employed by The Reg) so the power will be nothing.

#### Oh, the agony!

Is a raisin still a grape? What about raisin grapes? Are we talking about waterbomb-ey grapes from California? Or from Europe?

On a more serious note: what about the influence from the solar wind? Or is that negligible, compared to the effect described in the article?

#### Re: Oh, the agony!

Radiation pressure is much stronger than that produced by the solar wind (by about three orders of magnitude).

It's not negligible, however, and is taken into account when predicting the orbit of a GPS satellite to high precision, for example.

Unlike the solar wind, radiation pressure produces an off-axis force vector for a rotating body (in simple terms it gets hot, turns a bit, re-radiates as it cools).

#### Re: Oh, the agony!

Fuss, fuss pedantry...

Simple radiation pressure is an on-axis force, and it is radially oriented with respect to the primary, because it is just momentum transfer caused by the secondary absorbing or reflecting the outward radiation from the primary (presumed to be uniform). At the sub-micrometre level, radiation pressure from the Sun is strong enough to completely counter gravity, and such particles inevitably leave the Solar System

Yarkovsky effect forces are caused by the fact that part of the surface of a body is hot, while part is not-so-hot, and that those parts are not radially aligned. The hotter parts emit more photons, and so there is a net force. Depending on the speed and direction of rotation (and the size of the body - Yarkovsky effect is strongest in the 10m to 10km range), the object may be either slowed or speeded in its orbit, moving either in or out relative to the Sun.

The forces are small, but their effect is continuous and accumulative.

#### A 60g sample?

That's more than 12 grapes!

@AC Hamsters? 53 in a Watt? That's ridiculous! A supercharged AJV8 (Jag 5L) puts out 380kW in standard tune, that's 20.14 MHam.

If you carry the four and divide by the Watts you get 14 hamsters per horse!

The age old question, just how does one measure work? Spreadsheets produced? Time since last visit to El Reg?

#### Re: A 60g sample?

14 hamsters per horse!

\$units

2526 units, 72 prefixes, 56 nonlinear units

You have: 380e3*53 watt

You want: horsepower

* 27008.185

/ 3.7025813e-05

#### Re: how does one measure work?

I measure time to 5pm. Never close enough.

#### Re: A 60g sample?

1 horse = 750 watts

1 watt = 53 hamsters

=> 1 horse = 39,750 hamsters

I'm surprised you can only get ~19mW of work out of a hamster though. Lazy buggers.

#### Re: A 60g sample?

re 14 Hamsters per Horse - I guess it depends on the relative sizes of the two. Plus you could give the hamsters amphetamines.

#### Re: A 60g sample?

I'm hoping that on viewing the date and time posted you'll let me off on my incoherent arithmatic.

Pint because it's almost pint time.

#### rendezvous with the asteroid in 2019

hm, sounds like the asteroid will be someplace else by the time they get there.

#### It begins!

Sunshine? They would say that!

#### I'm surprised you didn't know...

The correct unit for force acting on a grape is the Francis. It is a derivative unit of the "Stu", which is the force required to crush a grape.

#### Re: I'm surprised you didn't know...

While applying the Francis pressure on the grape, does it make a "Oooo!" sound?

#### Re: I'm surprised you didn't know...

No. You only get an "Oooo!" with Typhoo.

#### Sour grapes?

So, how many grapes of force will be exerted on the asteroid by landing a probe on it, collecting a sample, and blasting off back to Earth? Wouldn't it be ironic if the orbital perturbation were just enough to change it from Earth-crossing to Earth-colliding.

#### Re: Sour grapes?

Hah! Let's see Alanis Morrisette get a rhyme out of, "Accidental perturbation of an asteroid's orbit, causing it to collide with our planet when it wouldn't have done had we not landed on it in the first place."

#### Re: Sour grapes?

Don't blame this slipping satellite... and, yes, is this scary? I am having trouble figuring out if it's meant to be scary.

Are we going to see Bruce Willis sent up on a Space Shuttle with a hundred rolls of metal baking foil, to wrap an asteroid up in reflective material and change its orbit?

#### Re: Sour grapes?

It's like the total annihilation of all known life,

On your wedding day when all you want is a knife.

#### Alanis Morrisette

Hmm...

"Like shifting an asteroid with a charged particle beam, isn't it ionic?"

#### Are they sure?

Are they sure that it's the Yarmovsky effect? For that, you'd presumably need to know it's absorbance / emitance parameters and it's rotational velocity to confirm that it is indeed due to the Yarmosvsky effect? I'm surprised that we know enough to say with certainty.

If we do the sums and it doesn't make sense, we'd have to attribute it to something else. Since Dark Matter® and Dark Energy® are already taken, perhaps we could call it Dark Magic?

#### Grapes ?

Only in space can three grapes push a 68-million ton rock

#### Re: Grapes ?

You only say that because YOU haven't seen those 3 grapes working out down at the gym with Hans and Franz.

... Shudder ...

AC cause I don't want to have to answer any question to THOSE grapes!

#### Half an ounce = 3 grapes ?!!

Didn't we have a Reg story a couple a days ago about NASA using SI units ? This is what I get for my suggestion that we should all convert instead to Plank units - I do abjure and forswear and take it all back - I'll be perfectly satisfied if we could all agree to use the Système international d'unités instead of grapes. If I've calculated right, the mass of those 3 grapes should exert a force at the Earth's surface of about 0.14 N, which is what I think Dr Chesley meant....

Henri

#### New Reg unit of distance

Based on the content of this story I propose a new unit of measurement for the Reg. The flyover. One flyover is the distance between New York and Los Angeles.

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