# Solar Wind and Asteroid orbital behavior

Can the solar wind affect the orbital elements of a nearby asteroid?

I would like to know if solar activity has an effect on the asteroid's orbit or gravitational stability and or can cause a gravitational disturbance to a meteoroid near the earth.

• affect? certainly. Significantly? depends on what you mean by "nearby' – Carl Witthoft Feb 9 '18 at 15:03
• I'm not what an orbital element is. Are you asking if the Sun can effect the asteroid's orbit or the asteroid's elements? – userLTK Feb 9 '18 at 15:45
• Thanks for your response. I would like to ask if the solar activities has an effect on the asteroid's orbit or gravitational stability and or can cause gravitational disturbance on the meteoroid near the earth. Thanks – Ron Feb 9 '18 at 16:55
• @userLTK Orbital Elements $-$ the set of parameter used to uniquely define an orbit. In other words, can these parameters be affected by the solar wind such that the asteroid is moved to a new orbit. – zephyr Feb 9 '18 at 22:22

## Sort of, via radiation pressure and heating.

The Sun emits photons, which carry with them energy and momentum. Any flux of photons applies pressure to an object it hits; this is the basic principle behind solar sails. In general, the larger the object, the more force it feels, since pressure is force per unit area. There are two main ways light from the Sun can significantly affect minor planets, such as asteroids:

1. The Yarkovsky effect: For a rotating body, there is a delay between when a portion of it receives heat and when the heat is re-radiated. The spinning object then has an offset between the angles of absorption and emission, which means that the radiation applies a net force. This can cause slow but steady changes; over 12 years, the asteroid 6489 Golevka deviated from its predicted orbital path for 15 kilometers.
2. The Yarkovsky–O'Keefe–Radzievskii–Paddack effect: The YORP effect occurs when irregularities in the surface of an object causes incoming light to be scattered in different directions. This changes the rotation direction and rate of the body. This has been observed in asteroids 54509 YORP (a rotational change of 250 degrees over four years) and 1862 Apollo.
• I was almost going to put this exact answer, but I didn't because I don't think the radiation actually counts as part of the solar wind. The solar wind is the set of baryonic particles outflowing from the Sun. While this effect is technically occurring, I don't think it actually answers the question as asked. – zephyr Feb 9 '18 at 22:16
• @zephyr I'm on the fence about it myself; I was inclined to keep it because it shows that normal solar activity does indeed influence the motions of asteroids, even in the absence of a solar wind. – HDE 226868 Feb 10 '18 at 0:38

I have lifted the text below from my currently unanswered question, (to which I've just added a bounty) Did Rosetta improve on models of non-gravitational effects on comet 67P's orbit? in another SE site. Based on the current unclearness of the distinction between comets and asteroids as discussed in @zephyr's colorful answer I'm going to leave it as is. (Is this object an asteroid or comet, and how can it produce so many tails? and its answer are also worth a look.) Objects "formerly known as" asteroids will not outgas as much as those known as comets, but the math and background may be helpful as an additional answer here. Of course @HDE's answer is nice and concise and to the point.

The Yarkovsky and Poynting-Robertson effects are mentioned below as well. It's clear these are included in the modeling of at least some asteroids, and comets.

The calculation of the orbits of comets can be more difficult than those of most asteroids for a number of reasons. Some comets have such highly eccentric orbits that aphelion is too far for the comet to be observed continuously, or the period is so long that only one pass has been observed and a period can not be calculated, or it passes so close to the sun that it's orbit is highly modified. However comet 67P/Churyumov–Gerasimenko currently has a period of only about 6.4 years a perihelion/aphelion of 1.2 AU and 5.7 AU respectively. While it's orbit is within a so called "frost line" it remains further from the sun than the Earth's orbit.

In this answer I plot some data from a recent NASA JPL Horizons ephemeris for comet 67P. The current default solution soln ref.= JPL#K084/25, data arc: 1995-07-03 to 2016-05-30 appears to use Marsden coefficients to model non-gravitational forces on the comet. Brian . Marsden was a British astronomer who contributed greatly to the field of cometary orbits. (See also here and here.) While exact modeling of non-gravitational forces on comets would be extremely complex, he introduced a simple empirical parameterization that provides a framework to discuss the magnitude and potential effects of these forces on the orbits of comets.

Using the following convention: $\hat{\mathbf{e}}_R, \ \hat{\mathbf{e}}_T, \ \hat{\mathbf{e}}_N$ are unit vectors at the location of the comet in the radial, transverse, and normal directions where $\hat{\mathbf{e}}_R$ points away from the sun, $\hat{\mathbf{e}}_N$ is the direction of the angular momentum vector (perpendicular to the orbit plane) and $\hat{\mathbf{e}}_T$ is perpendicular to the first two and approximately in the direction of motion, non-gravitational accelerations can be parameterized using the empirical equations:

$$\mathbf{a}_{NG} = ( A_1\hat{\mathbf{e}}_R \ + \ A_2\hat{\mathbf{e}}_T \ + \ A_3\hat{\mathbf{e}}_N) \ g(r),$$

where:

$$g(r)= 0.111262\left(\frac{r}{2.808}\right)^{-2.15} \left(1+\left(\frac{r}{2.808}\right)^{5.093}\right)^{-4.6142},$$

and the acceleration coeficients $A_1,A_2,A_3$ commonly have units of $AU / day^2$.

I've reproduced these here to illustrate the basic idea. There are further considerations including a delay term and effects of rotation. However with this parameterization it is possible to discuss and at least get a handle on non-gravitational effects without a detailed physical model. These effects might the Yarkovsky and Poynting-Robertson effects, and of course recoil from material energetically ejected from the comet, especially as it approaches the sun and is heated.

The parameters $A_1,A_2,A_3$ in model can be used to express effects from physical models of comets, but they can also be used as fitting parameters to improve orbital solutions for comets based on observational data.

above: linear and semi-log plots of $g(r)$ between 1.2 and 5.7 AU.

above: Example of the non-gravitational parameters used in the most recent JPL Horizons ephemeris for comet 67P. The coefficients have units of $AU/day^2$. For a comparison, the gravitational acceleration at a distance of 1.2 $AU$ is about 0.0041 $m/s^2$ or about 2.1E-04 $AU/day^2$. This suggests that the non-gravitational forces used here have a parts-per-million effect per orbit which will become substantial over a large number of orbits.

• Thank you very much. Your answers helped me a lot. I am planning to do a scientific research regarding on this matter, but I really don't know where to start, that's why I started to read some published Journals. Just want to ask if you know someone who could help or willing to mentor me in my endeavor. Thank you very much – Ron Feb 11 '18 at 11:21
• @Ron Stack Exchange is not really for leaving personal messages. It's best to stick to the Question and Answer format. I'd recommend you delete your e-mail address here. – uhoh Feb 11 '18 at 12:03
• @Ron there is a chat room for Astronomy SE, and one for Space Exploration SE as well. You can chat with others there and you will find a wide variety of people with different expertise. The room in Space Exploration is much more active, so I would suggest starting there first. You can use the same "@" symbol in front of users names there, then they will receive a notification of your message. – uhoh Feb 11 '18 at 12:13