Newly Discovered House-Sized Asteroid 2017 HX4 Flew Safely Past the Earth Yesterday

Yesterday (on May 8th, 2017), an asteroid swung past Earth on its way towards the Sun. This Near Earth Object (NEO), known as 2017 HX4, measures between 10 and 33 meters (32.8 and 108 feet) and made its closest approach to Earth at 11:58 am UT (7:58 am EDT; 4:58 am PT). Naturally, there were surely those who wondered if this asteroid would hit us and trigger a terrible cataclysm!

But of course, like most NEOs that periodically make a close pass to Earth, 2017 HX4 passed us by at a very safe distance. In fact, the asteroid’s closest approach to Earth was estimated to be at a distance of 3.7 Lunar Distances (LD) – i.e. almost four times the distance between the Earth and the Moon. This, and other pertinent information was tweeted in advance by the International Astronomical Union’s Minor Planet Center (IAU MPC) on April 29th.

This object was first spotted on April 26th, 2017, using the 1.8 meter Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), located at the summit of Haleakala in Hawaii. Since that time, it has been monitored by multiple telescopes around the world, and its tracking data and information about its orbit and other characteristics has been provided by the IAU MPC.

Interactive Orbit Sketch, showing the orbit of the Near Earth Object (NEO) known as 2017 HX4. Credit: IAU MPC

With funding provided by NASA’s Near-Earth Object Observations program, the IAU MPC maintains a centralized database that is responsible for the identification, designation and orbit computations of all the minor planets, comets and outer satellites of the Solar System. Since it’s inception, it has been maintaining information on 16,202 Near-Earth Objects, 729,626 Minor Planets, and 3,976 comets.

But it is the NEOs that are of particular interest, since they periodically make close approaches to Earth. In the case of 2017 HX4, the object has been shown to have an orbital period of 2.37 years, following a path that takes it from beyond the orbit of Venus to well beyond the orbit of Mars. In other words, it orbits our Sun at an average distance (semi-major axis) of 1.776 AU, ranging from about 0.88 AU at perihelion to 2.669 AU at aphelion.

Since it was first spotted, the object has been viewed a total of 41 times between April 26th and May 4th. In addition to the Pan-STARRS-1 survey, observations were also provided by the Cerro Tololo Observatory, the Mauna Kea Observatories, the Steward Observatory and the Kitt Peak-Spacewatch Telescopes, the Astronomical Research Observatory, the Apache Point Observatory, and the Mount John Observatory.

PS1 at dawn. The mountain in the distance is Mauna Kea, about 130 kilometers southeast. Credit: pan-starrs.ifa.hawaii.edu

From these combined observations, the IAU MPC was able to compile information on the object’s orbital period, when it would cross Earth’s orbit, and just how close it would come to us in the process. So, as always, there was nothing to worry about here folks. These objects are always spotted before they cross Earth’s orbit, and their paths, periods and velocities and are known about in advance.

Even so, it’s worth noting that an object of this size was nowhere near to be large enough to cause an Extinction Level Event. In fact, the asteroid that struck Earth 65 millions year ago at the end of Cretaceous era – which created the Chicxulub Crater on the Yucatan Peninsula in Mexico and caused the extinction of the dinosaurs – was estimated to measure 10 km across.

At 10 to 33 meters (32.8 to 108 feet), this asteroid would certainly have caused considerable damage if it hit us. But the results would not exactly have been cataclysmic. Still, it might not be too soon to consider getting off this ball of rock. You know, before – as Hawking has warned – a single event is able to claim all of humanity in one fell swoop!

The MPC is currently tracking the 13 NEOs that were discovered during the month of May alone, and that’s just so far. Expect to hear more about rocks that might cross our path in the future.

Further Reading: IAU Minor Planet Center

Asteroid 2014 SC324 Zips By Earth Friday Afternoon – Tips on How to See it

What a roller coaster week it’s been. If partial eclipses and giant sunspots aren’t your thing, how about a close flyby of an Earth-approaching asteroid?  2014 SC324 was discovered on September 30 this year by the Mt. Lemmon Survey high in the Catalina Mountains north of Tucson, Arizona. Based on brightness, the tumbling rock’s size is estimated at around 197 feet (60-m), on the large side compared to the many small asteroids that whip harmlessly by Earth each year.

Near-Earth asteroid 2014 SC324 caught in the camera on October 23. The telescope tracked on the zippy space rock, causing the stars to trail. Credit: Gianluca Masi
Near-Earth asteroid 2014 SC324 caught in the camera on October 23. The telescope tracked on the zippy space rock, causing the stars to trail. Credit: Gianluca Masi

Closest approach happens around 2 p.m. CDT (7 p.m. UT) Friday afternoon when our fast friend misses Earth by just 351,000 miles (565,000 km) or 1.5 times the distance to the Moon. This is a very safe distance, so we can finish up our lunches without a jot of concern. But the asteroid’s  combination of size and proximity means amateur astronomers with a 10-inch or larger telescope will be able to track it across the sky beginning tonight (Oct. 23) and continuing through tomorrow night. 2014 SC324 should shine tolerably bright this evening at around magnitude +13.5.

Bright here is something of a euphemism, but when it comes to new Earth-approaching asteroids, this is within range of many amateur instruments. And because 2014 SC324 is “only” a half million miles away tonight, it’s not moving so fast that you can’t plot its arc on a single star chart, spot it and go for a ride.


Simulation based on recent data showing the known asteroids orbiting the Sun

By Friday evening, the new visitor will have faded a bit to magnitude +14. You can create a track for 2014 SC324 by inputting its orbital elements into a variety of astro software programs like MegaStar, the Sky, and Le Ciel. Elements are available via the Minor Planet Center and Horizons. Once saved, the program will make a track of the asteroid’s movement at selected time intervals. Print out the chart and you’re ready for the hunt!

Illustration of small asteroids passing near Earth. Credit: ESA / P. Carril
Illustration of small asteroids passing near Earth. Credit: ESA / P. Carril

You can also go to Horizons, ask for a list of positions every 15 minutes for example and then hand plot those positions in right ascension (R.A.) and declination (Dec.) on a star map.  This is what I do. I find the the general chunk of sky the asteroid’s passing through, print the map and then mark positions in pencil and connect them all with a line. Now I’ve got a chart I can use at the telescope based on the most current orbit.

Tonight the errant mountain will rumble through Aries the Ram, which is conveniently located in the eastern sky below Andromeda and the Great Square of Pegasus at nightfall.

Finding a dim, fast-moving object is doubtless an exciting challenge, but if you lack the equipment or the weather doesn’t cooperate, you can see the show online courtesy of Italian astrophysicist Gianluca Masi. He’ll stream the close encounter live on his Virtual Telescope Project website beginning at 7 p.m. CDT (midnight UT) tomorrow night October 24-25.

Clear skies!