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Apophis is a near-Earth asteroid with a diameter of metres that caused a brief period of concern in December because initial observations indicated a.
Table of contents
- Ephemeris Calculator
- Apophis - Wikipedia
- Huge Asteroid Apophis Flies By Earth on Friday the 13th in 2029. A Lucky Day for Scientists
If Asteroid Apophis arrived in the skies over Earth today, the brute force of impact would likely kill untold millions of people. As a result, the US space agency has determined 10 dates on which there is a calculable risk of deadly impact. If Apophis ends up hitting the planet on any of these dates, NASA said the force of impact would be equivalent to 1, megatons or 1,, kilotons of kinetic energy. For comparison, the US atomic bomb dropped on Hiroshima in detonated with the force of around 15 kilotons of TNT.
NASA predicts 10 dates between and on which there is a small chance Apophis will veer off its path and into Earth. On any of these dates, NASA estimates the space rock would fly into our planet at speeds of about 5. At the point of atmospheric entry, the asteroid would then speed up to about By observing Apophis during its flyby, we will gain important scientific knowledge.
Ephemeris Calculator
The space rock was first discovered on June 19, , and astronomers initially feared Apophis could hit Earth during a close flyby in Even South African billionaire and SpaceX founder Elon Musk has expressed concerns about the possibility of an asteroid striking Earth. Then on November 14 he also ominously retweeted a predicted trajectory map of Asteroid Apophis near-missing Earth in Officially dubbed by astronomers Apophis or MN4, the giant space rock has been a keen object of study since its discovery 15 years ago.
Thankfully, NASA is yet to sound the alarm bells as there appears to be no significant risk of impact just yet.
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In April , there is a very small chance the space rock will divert its orbit straight into our home planet. In other words, there is a 0. There is a slightly higher chance of impact in with NASA giving the asteroid odds of about one-in The odds translate to a 0. According to the Planetary Society, you should not lose any sleep over the threat of asteroid impacts.
Lhotka 2 , G. Heron 1 , Y. Puente 4 and M. Folgueira Lopez 4. Received: 27 February Accepted: 13 May The dramatic event of the close encounter between the Earth and the asteroid Apophis on April 13 at a minimum distance of 38 km constitutes an opportunity to make investigations about the modeling of the rotational changes of the asteroid during the event. In this paper we deepen a previous study of the rotational changes of Apophis caused by gravitational effects during the close encounter, using important constraints on initial conditions brought by new recent observational data.
We also evaluate the effects of the triaxial form of the asteroid on the motion of its axis of rotation in space, as well as the modifications of the spin rate due to tidal deformation. First we used more drastic constraints for the physical and geometrical parameters of Apophis, deduced from recent observational campaigns. Second we evaluated the disturbing potential due to the Earth depending not only on the asteroid flattening, but also on the component due to its triaxiality, to deduce the equations of motion and investigate the displacement of the spin axis.
Third we estimated what should be the zonal deformation of the asteroid due to the tide exerted by the Earth during the close encounter and we measured the consequences on variations of the spin rate. On the contrary, effects on the spin rate should be relatively small, leading to variations of the sidereal angle of rotation not exceeding 30 s. The tribute of this paper is to give a constrained model of the important rotational variations of Apophis during its close encounter with the Earth. For the circumstances of this discovery we refer the reader to a detailed report by Giorgini et al.
By using these ephemerides, Souchay et al. The values, presented in Table 1 , show the dramatic changes undergone by these parameters due to the gravitational perturbation of our planet during the CE. We note that some other close encounters are forecast on , and , with risks of collision which can be considered as negligible. Nevertheless the estimation of these risks seems to be strongly affected by the Yarkovsky effect Bottke et al. Models are refined with the input of new observational data Bancelin et al. Table 1.
Orbital parameters of the asteroid Apophis before and after the close encounter with the Earth, taken from Souchay et al. In addition to large orbital changes during the CE, Apophis should also undergo significant modifications of its rotational state, as already demonstrated by Scheeres et al. As in the case of any celestial body this rotational state can be defined by three main components: the first is the locus of the axis of rotation or of figure in space; the second is the angular rotational velocity of the asteroid around its rotational axis.
A third component is characterized by the motion of the instantaneous axis of rotation with respect to a body-fixed frame. The first component is classically called the combined precession-nutation motion, whereas the second one is directly associated, with the help of a simple integration, to the sidereal angle of rotation. Scheeres et al.
Apophis - Wikipedia
For the purpose they carried out a Monte Carlo simulation involving flyby geometry in the body fixed space, the moments of inertia and the initial rotation state of the asteroid. Their results were essentially qualitative, with unknown fundamental parameters as the value of the moments of inertia, and the initial nature of the rotational status short or long axis mode.
Nevertheless, their results clearly show that the probability that the rotation be and remains in a short axis mode during the CE is very high. We note that their study concerns the second and third components of the rotation mentioned above. In complement, Souchay et al. For this purpose the model is deterministic, based on a Hamiltonian theory for a solid rotational body Kinoshita previously applied with good precision for terrestrial planets Souchay et al.
In these studies the equations of motion are given in a rather straightforward manner, depending on a set of a few fundamental parameters, defined in detail in Sect. Among these parameters are the initial value of the obliquity of the asteroid and the values of its moments of inertia, which were still unknown when the study was published. This paper is highly motivated by new knowledge of the parameters above, due to recent investigations Pravec et al.
In Sect.
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Section 3 is devoted to the explanation of the parametrization adequate for our theoretical developments. From that we can deduce the equations of motion of Apophis angular momentum axis in space. Then we integrate these equations numerically to measure the amplitude of this last motion during the close encouter. As a complementary study, we evaluate in Sect. Previous studies concerning the rotational changes of Apophis during the CE Scheeres et al. In particular fundamental parameters for the calculations as the values of the moments of inertia and the positioning of the spin axis at some given date were not available.
The situation has drastically changed since a recent study by Pravec et al. For instance the authors showed that Apophis rotation is retrograde, and that should have interesting implications for impact predictions.
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For instance Farnochhia et al. For such a study thermal effects depending on the rotational regime are dominant. First, Pravec et al. As a consequence, from the rotation light-curves the authors deduced that the asteroid is in a moderately excited short axis mode SAM. According to Pravec et al. The calculations of the perturbing rotational potential exerted by the Earth on Apophis during the CE necessitates the adoption of a conventional inertial reference plane.
As already explained in similar rotational studies, for instance Lhotka et al. This considerably simplifies the calculation of the perturbing gravitational potential. For the study above, by far the predominant perturbing body was the Sun. Therefore the reference plane was the orbital plane of the asteroid considered around the Sun. In the case we consider here the close encounter of the asteroid with the Earth the reference plane is the relative orbital plane of the Earth with respect to Apophis centre of mass.
Thus, let us call [ P 0 ] the osculating relative orbital plane of the Earth with respect to the Apophis centre of mass during the CE. We note that the rotation of Apophis is retrograde, as well as the relative orbital motion of the Earth related to the asteroid centre of mass.
We have reversed the geometry Fig. Moreover from [ P 0 ] two parameters are suffcient to represent the relative motion of our planet with respect to the centre of mass of the asteroid Fig.
Huge Asteroid Apophis Flies By Earth on Friday the 13th in 2029. A Lucky Day for Scientists
Concerning these two last variables, Souchay et al. We normalize r t to be of unit length. The results are shown in Fig. The dotted line corresponds to the nominal value in this paper, mentioned in the figure. The grey bin corresponds to the peak of the distribution. To calculate the variations of the orientation of Apophis angular momentum during the CE, we were able to use the classical theory of Kinoshita for the rotation of a rigid body here Apophis undergoing the gravitational potential exerted by an external body here the Earth. The represent the Legendre polynomials of degree i and order j.
Here we restrict to the first order part U 1 of the potential.