Posts Tagged ‘Фотометрия астероидов’

Earth and Moon changed orbit of near-Earth asteroid 2012 TC4

Detlev Van Rawenswaay / Science Photo Library

On 12 October 2012, 5:30 UTC, an asteroid 2012 TC4 (which I discussed earlier) made a close approach at 95 000 km from Earth. Its photometric observations were conducted at out observatory 24 hours before the closest approach. During the observations, the asteroid got closer to our planet from 583 400 to 508 600 kilometers. Accuired data allowed to estimate its rotational period, which is 12.2 minutes. More detailed data, as well as the magnitude graph, will be published in the Minor Planet Bulletin. Fast rotation of such small cosmic bodies that come close to Earth is common, and serves as proof of their origin from collisions. I should note that the period of 12.2 minutes isn’t the shortest among asteroids observed at ISON-NM observatory. For example, rotation period of another asteroid – 2012 KP24 is just 2.5 minutes! Absolute record at the moment belongs to the asteroid 2010 TD54, it makes a full rotation in just 42 seconds!

The analysis of evolution of the orbit of asteroid 2012 TC4 during its close approach to Earth shows that its orbit was affected by the gravitational influence of the Earth-Moon system. In the XY plane (in this case the ecliptic plane), the asteroid’s orbit was deflected by ~13 degrees from its original direction. The orbital period of 2012 TC4 around the Sun increased by 20%, from 1.45 to 1.74 years. The graph below shows this. The next close approach of this asteroid with Earth will happen in 5 years.

Translation by Maksim Kakitsev.

(Russian) В сентября нас ждет пролет яркого околоземного астероида

14 сентября 2012 года, в 9:13 утра, мимо Земли пролетит достаточно крупный объект – недавно открытый астероид 2012 QG42. В момент максимального сближения, дистанция до него составит свыше 2 840 000 км, что абсолютно безопасно для жителей Земли. Максимального видимого блеска, 13.8 звездной величины, астероид достигнет двумя днями ранее. Хотя подобные астероиды считаются яркими и их пролеты достаточно редки, этого гостя смогут увидеть лишь астрономы-любители, обладающие крупными любительскими телескопа, вдали от городов.

“Blinking” asteroid passes the Earth

This interesting near-Earth asteroid was discovered by the Spanish La Carpa survey on April 8th, receiving the designation 2011 GP59. Several hours after the discovery of the object, one of its discoverers, Jaime Nomen reported that the object noticeably varied in brightness with an amplitude of more than two magnitudes! This is very significant; most asteroids, due to their rotation, vary in brightness by tenths of a magnitude.

Lowell observatory / Brian Skiff

Many asteroid observers have observed this new guest, and we have received precise photometric curves (graphs of the change in brightness with time). One of the astronomers was Brian Skiff, working at Lowell Observatory. You can see the graph at left.

The period of rotation of asteroid 2011 GP59 is just 7.5 minutes, although this is far from the fastest rotating asteroid. The record belongs to asteroid 2010 TD54; it makes a full rotation on its axis in just 42 seconds!

Above, you can easily see how asteroid 2011 GP59 “blinks”. This animation was made by Nick James using his 28-cm telescope. At the time of the image, the asteroid was located 3,356,000 km from Earth – 1.4 times the average distance from the Earth to the Moon. Its closest distance to the Moon on this passage was 2.3 times less than that- just 236,000 km. The next time this asteroid passes by the Earth will be April 9, 2028.

The search for binary asteroids in the population of NEAs

Since the beginning of the work at our observatory, one of our basic tasks has been the job of photometric studies of near Earth asteroids (NEAs). At the end of October observations were made of several bright asteroids, including asteroid 3122 Florence which our team has been observing since Summer at several observatories. The asteroid belongs to the Amor group like the first NEA we discovered, 2010 RN80, and is potentially hazardous to our planet (Potentially Hazardous Asteroid, PHA). The period of the asteroid is already precisely known; it is 2.3581 hours. In the graph at left you can see its phase curve from observations obtained October 28-29 at our observatory.

Our main task is the determination of the angle of its rotation axis and, of course, searching for possible satellites. For that it is necessary to determine a second or even third period within the basic one, all tied to the rotation of the main body. For this painstaking work, high precision photometric observations are needed at various phase angles at several oppositions. This is not a task for one year.

Photometry of asteroids is more complex than observing variable stars, as the asteroids move quickly in space, especially near Earth asteroids. Because of that, from night to night, observations are made using different comparison stars, which complicates the task. It is also necessary to calculate the phase angle. Brightness curves obtained on different nights will slightly differ one from another, and to determine a phase curve, it is necessary to take out the brightness differences associated with the spatial effect (distance from the observer, phase angle), but not the rotation of the asteroid on its axis, as well as the possible orbital motion of a satellite.

Here you can become acquainted with the paper about the discovery of the satellite of asteroid 8373 Stephengould.

More detail information about our photometry program you can find on this page.

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