Impact: Detection of Near Earth Objects and Preventing a Collision

Near Earth Object or NEOs refers to comets or asteroids with orbits that enter Earth’s neighbourhood. More specifically, these comets or asteroids are at a distance of less than 1.3AU or 19,477,323 km, at the point of orbit closest to the sun.³ Many NEOs are asteroids.³

When a NEO is an asteroid it is referred to as a Near Earth Asteroid or NEA. These NEAs are separated into three groups based on the NEAs distance to the sun³, as seen in Figure 1. 

Potentially Hazardous Objects or PHOs are asteroids, and less often comets, that are significantly large and close enough to Earth to pose a serious threat of collision.  NEOs with orbits that come within 0.05 AU to Earth and are at least 150 m in diameter are considered threatening.⁴

The location of Near Earth Objects like NEAs is of great importance to humans. While there is a low probability of a large NEA impacting Earth, the consequences of such an impact are very high.⁵ It is critical that threats are detected years before getting close to Earth.⁶ Detection is the first step in preventing an impact with Earth.

The three most successful discovery survey programs (i.e detection programs) for NEAs since 1995 are the LINEAR Program, The Catalina Sky Survey  and Pan-STARRS, where the latter two account for 90% of new NEO discoveries.²⁶

Less influential but still important are Spacewatch, NEOWISE, NEAT, and LONEOS.⁷ These programs will be discussed below.

In 2005, NASA was tasked with detecting 90% of Near-Earth objects with a size greater than 140 meters in diameter by the year 2020.⁸

Why use infrared telescopes?

When observing the night sky from here on Earth, either with the naked eye or with an optical telescope, bright stars and planets are seen easily, even the occasional asteroid or comet is observed given they have a reflective enough surface. When the goal is to find dim, less reflective NEOs, bright stars outshine objects of interest in the visual wavelengths of the energy spectrum, however, thermal radiation in the infrared spectrum is readily emitted.²⁷ As the name suggests, infrared telescopes scan in the infrared band of the electromagnetic spectrum²⁷, thus making them ideal for detecting NEOs while ignoring visually bright stars. Infrared telescopes are essential to NEO detection efforts. Often, comets and asteroids are initially detected by infrared telescopes, which then have follow-up observations performed by ground-based optical telescopes.²⁷

The Lincoln Near-Earth Asteroid Research (LINEAR) program is funded by the United States Air Force and NASA and is comprised of two one-meter Ground-Based Electro-Optical Deep Space Surveillance (GEODSS) telescopes located at Lincoln Laboratory Experimental Test Site in Socorro, New Mexico, USA.⁹ LINEAR is a new application for technology originally used to detect Earth-orbiting satellites.⁹ Since its inception in 1998, LINEAR has contributed to the detection of many NEOs.⁹ Major changes to the system were needed to catalogue more asteroid populations of smaller sizes (down to 140m) which was accomplished in 2014 when the LINEAR program was successfully transitioned from two 1-m telescopes to a 3.5-m wide-field-of-view Space Surveillance Telescope (SST) at the Atom Site on White Sands Missile Range, New Mexico.⁹

The Catalina Sky Survey (CSS) began operating in April 1998 at Mt. Lemmon Observatory and in 2013, the program added a second reflecting telescope at the same location.¹² CSS is very accurate at detecting NEOs; in 2012 the program was responsible for the detection of more than 625 NEOs.¹² The success can be partly accredited to the wide-ranging sky coverage, and the subsequent follow-up observations, made by the Mt. Lemmon telescope. The CSS’s success in detection has contributed to making it more popular as its exploration progressed. This popularity has added to its importance in detecting NEOs.

The Panoramic Survey Telescope and Rapid Response System or Pan-STARRS was developed at the University of Hawaii Institute for Astronomy and full-time, continuous, scientific observations began May 13, 2010.⁸ Discovering and characterising PHOs is the main goal of Pan-STARRS and it is able to detect objects 100 times fainter than other detection programs.⁸

Pan-STARS at sunset
Forest Starr and Kim Starr

NEOWISE is an infrared space telescope funded by NASA’s planetary science division and is the asteroid detection specific portion of NASA’s WISE program.¹⁴ In December 2013, NEOWISE was brought out of hibernation to aid in the detection of PHOs.¹⁴ Currently, NEOWISE is about 70% of the way through its sixth coverage of the entire sky.¹⁴

This artist's concept shows the Wide-field Infrared Survey Explorer, or WISE spacecraft, in its orbit around Earth.
NASA/JPL-Caltech

LONEOS or The Lowell Observatory Near-Earth-Object Search has the capability to scan the entire assessable sky every month and is located in Flagstaff, Arizona.¹³ It consists of a 0.6m fully-automated Schmidt telescope and CCD camera imaging device capable of recording asteroids and stars 150,000 times fainter than can be seen with the human eye in just one minute of exposure.¹³

The Near Earth Asteroid Tracking (NEAT) began in December 1995 and ran observations every month until 2007. The system operated autonomously at the Maui Space Surveillance Site on the summit of the extinct Haleakala Volcano Crater, Hawaii.¹¹ While the program was discontinued in 2007²⁸,  NEAT contributed 26,000 detections of main-belt asteroids.¹¹

Spacewatch began in 1983 under the counsel of Tom Gehrels. The 0.9m f/5 Newtonian telescope was the backbone of the first lengthy CCD discovery program.¹⁰ Spacewatch was the first program to discover a NEO using automated image processing software and was also the original program to utilise CCD technology in the discovery of NEOs.¹⁰ Through 2008, Spacewatch gradually shifted their emphasis from NEO detections to follow-up observations that are critical for securing accurate orbits and monitoring numerous small object populations. Additionally, the focus of Spacewatch has also spread to the detection of potential interplanetary space missions.¹⁰

Announced in 2012, the Sentinel Space Telescope will be designed and built for the B612 Foundation which is dedicated to protecting Earth from dangerous asteroid impacts. The Sentinel is an infrared telescope with a tentative launch date in 2019 and is being designed to locate 90% of known asteroids greater than 140 m in diameter in near-Earth orbits.¹⁵

Large Synoptic Survey Telescope (LSST) began construction in August 2014 and is expected to be completed by 2019. Its design is a large-aperture wide-field, ground-based telescope that will survey half the sky every few nights. The design will use three mirrors instead of the

Three-dimensional rendering of the baseline design for the LSST
LSST

conventional two in order to produce a very wide, undistorted field of view. Once completed, the telescope will potentially be able to detect asteroids as small as 140 m in diameter and as far away as the Main Belt asteroids. It is projected to detect 60-90% of potentially hazardous asteroids larger than 140 m.¹⁶

Currently, the various deflection mechanisms proposed are not cost-effective enough to be feasibly implemented as a mitigation strategy against cosmic threats.  However, some of these techniques have shown promising results in their hypothetical abilities to divert PHOs.¹⁷ These deflection mechanisms include Thermonuclear Devices, Directed Energy Systems, and Kinetic Impactors. 

Kinetic Impactor works by sending one or more large, fast moving spacecraft to intersect the path of approaching NEOs. The proximity and mass of the spacecraft will exert a gravitational attraction which can change the trajectory of the NEO, deflecting it away from Earth’s orbital path.²⁵ Advanced warning would be needed to implement a kinetic impactor, approximately 1 – 2 years of warning would be necessary for small asteroids and upwards of 10 years would be necessary deflect a large (100+ km diameter) object.²⁵ This may not be effective in changing the orbits of the larger objects due to the amount of energy needed to do so.

Photo from the Deep Impact Mission where a kinetic impactor was used to gather data about a comet. This would be the type of impactor proposed to divert NEOs.
Courtesy of NASA

Directed Energy Systems (DES) would utilise laser energy to essentially vaporise a PHO’s materials, either abolishing them or using the ablation to change the object's trajectory.²⁴ It is a proposed system that is currently applied for military use, and hypothetically, could deflect all known threats with sufficient warning.²⁴ Two classifications of laser systems exist, DE-STAR (Directed Energy System for Targeting of Asteroids and exploRation) and DE-STARLITE(Directed Energy System for Targeting of Asteroid and exploration LITE). DE-STAR, also known as “stand-off” modular phased arrays, would focus kilowatt class lasers on PHOs with the purpose of vaporising the object.²⁴ DE-STARLITE would be a smaller “stand-on” system stationed on a modest spacecraft while moving in accordance with the asteroid. It is a lengthier process and more mobile than the DE-STAR system which would remain situated within Earth’s orbit.²⁴

Thermonuclear devices (TND) are weapons that use heat or nuclear power as their source of energy. As the name indicates, the main goal is to use this nuclear energy to change the direction of the trajectory of a PHO so that it does not collide with Earth. There is evidence that nuclear weapons can be efficient in protecting Earth from PHOs²², but the size of the object would be a limiting factor. A small enough object could be diverted by nuclear weapons, but for larger objects, it would be harder to get the amount of nuclear power needed to divert them.²²

A depiction of Excalibur, an interspace Thermonuclear Device for missile defence, firing on a single object. Similar technology is proposed to divert PHOs.
Courtesy U.S Airforce

Humans have an ethical obligation to prevent harm when and where it is possible to do so, and as such the appropriate thing to do is be prepared for an impact with a PHO. Detection of NEOs is and always will be step one of the moderation process. Without detection, there is no chance of mitigation. By 2020, detection of objects larger than 140m is to be completed by NASA programs, adding to the ability to defend the Earth from an impact. Moving forward, more educational materials need to be made available to the public, and hopefully, this site can aid in that goal. Further global warning systems and disaster plans need to be negotiated internationally, and short-term mitigation systems need to researched and tested, as touched on in the discussion of the READI Program.  As life on Earth advances, so should the interest in preserving that life from both threats here on Earth and those existing in the vastness of space.