By: Andrea Alas, Astrid Alas, Caleb Dueck, Sarah Huynh, David Lu, Cornelia Nagel
There are thousands of asteroids and comets orbiting throughout the solar system right now. Those that travel close to Earth are known as Near Earth Objects or NEOs. A vast majority of these extra-terrestrial objects pose no threat to life on Earth, but at times these bodies drift into Earth’s vicinity and become a cause for concern. There are many programs aimed at the detection of these Near Earth Objects with the hopes of discovering threats with ample time to avoid catastrophe. Detection is the first step towards prevention, and as such the hunt for NEOs begins with an exploration of past and present detection programs, and a consideration of proposed future programs and technologies. The available preventative measures are hypothetical at this stage, but they generally focus on deflection systems. Should a NEO become a danger to Earth, its trajectory could be changed using one of the examined deflection techniques, safeguarding life as we know it. Better detection will result in more proactive and preventative measures to counter against devastating collisions.
Comets: Space objects made of frozen gases, rocks and dust, sometimes referred to as "frozen snowballs."1
Asteroids: Space objects of various sizes made of rocks and metals that are too small to be considered planets.2
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
How are Near Earth Objects Detected?
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
Current Principle Discovery Programs
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
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
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
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
How Dangerous are Asteroids?
Of the Near Earth Objects detected, few are actually of any threat to life on Earth. Threatening asteroids, i.e. PHOs, are classified as being approximately 20m to 500m in diameter.23 Currently, no serious risk to Earth has been detected for the next 100 years or so, however, new smaller potentially harmful objects are still being discovered.3 The most efficient, safe, and energy efficient strategy against a short warning PHO is to divert it from its trajectory.23 Diversion is the preferred mitigation technique because destruction would result in the dispersal of asteroid fragments leading to a larger number of possible PHOs with unpredictable trajectories. 23 The deflection option depends on the time to impact, as well as the size, type, composition, and the trajectory of the PHO that is approaching Earth.
As suggested above, the chances of a large PHO striking Earth is very unlikely, but the repercussions are far reaching.21 Often, the object burns up in Earth’s atmosphere, but occasionally, large enough objects (i.e larger than 20m23) enter Earth's atmosphere and make an impact with Earth. Even if the meteor doesn’t make an impact with Earth or is relatively small, the energy released is comparable to that of an atomic bomb,17 such as that seen in Chelyabinsk, Russia in 2013. It is estimated that the meteor that impacted in Chelyabinsk “exploded with the energy of 500 Kilotonnes”.18 For comparison, the atomic bombs dropped on Hiroshima and Nagasaki only had an energy equivalent of 16 Kilotonnes.19 If the object is large enough, the devastation would be imminent. The Chicxulub Crater, located in the Yucatan Peninsula of Mexico, is an estimated 65 million years old.20 Officially discovered some 30 years ago, it is thought to be responsible for the eventual extinction of many species, including the dinosaurs.17
Impact: Detection to Deflection
The Roadmap for Earth Defense Initiatives (READI Project) is a planetary defence project created during the International Space University Studies Program in 2015. It creates ‘roadmaps’, or plans, for space agencies, governments, and the general public, to deal with astronomical emergencies in situations where PHOs cannot be destroyed due to short warnings.21
READI Consists of five elements of Planetary Defense21:
- Detection of PHOs followed by a tracking phase
- Deflection of PHOs via thermonuclear devices (TED) and the Directed Energy System (DES); the safest and most efficient means of PHO impact prevention
- Global Collaboration where new norms, legal actions, and an advisory body are implemented into the Planetary Defense Program for imminent impact threats
- Outreach and Education to better educate and increase the interest in Planetary Defense amongst children and students;
- Evacuation and Recovery strategies that target different situations and threat characteristics according to the type of asteroid and comet impact response
READI mainly focuses on deflection and disruption methods against PHOs and approaches the problem of an incoming PHO with a warning period of approximately two years from detection to impact with Earth.21 This page discusses detection, deflection, and a few points concerning global collaboration. Readers interested in outreach and education, and evacuation and recovery strategies are encouraged to read Architecture for Mitigating Short-Term Warning Cosmic Threats: READI Project.
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.
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
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.
1Qualitative Reasoning Group, “What is a Comet?,” Space Environment, 2015, https://www.pierce.ctc.edu/library/ref/files/aip_citations.pdf
2Cool Cosmos, “What are Asteroids?,” Ask an Astronomer, 16 August 2013, http://coolcosmos.ipac.caltech.edu/page/what_is_infrared
3National Aeronautics and Space Administration, “Neo Groups,” Near Earth Object Program, http://neo.jpl.nasa.gov/neo/groups.html
4National Space Society, “Report of the Task Force on potentially hazardous Near Earth Objects,” Planetary Defense Library, September 2000, http://www.nss.org/resources/library/planetarydefense/2000-ReportOfTheTaskForceOnPotentiallyHazardousNearEarthObjects-UK.pdf
5National Aeronautics and Space Administration, “Catalog of Known Near-Earth Asteroids Tops 15,000,” Jet Propulsion Laboratory, 27 October 2016, http://www.jpl.nasa.gov/news/news.php?feature=6664
6National Aeronautics and Space Administration, “Target Earth,” Near Earth Object Program, http://neo.jpl.nasa.gov/neo/target.html
7National Aeronautics and Space Administration, “Number of Near-Earth Asteroids Discovered,” Near Earth Object Program, http://neo.jpl.nasa.gov/stats/
8University of Hawaii, “Panoramic Survey Telescope & Rapid Response System,” Institute for Astronomy, 2005, http://pan-starrs.ifa.hawaii.edu/public/home.html
9Massachusetts Institute of Technology, “LINEAR,” Lincoln Laboratory, 2016, http://www.ll.mit.edu/mission/space/linear/
10 The University of Arizona, “Spacewatch,” Lunar and Planetary Laboratory, 03 June 2016, http://spacewatch.lpl.arizona.edu/
11 National Aeronautics and Space Administration, “Near Earth Asteroid Tracking,” http://neat.jpl.nasa.gov
12 National Aeronautics and Space Administration, “Catalina Sky Survey,” Near Earth Object Program, 2016, http://neo.jpl.nasa.gov/programs/css.html
13 The Lowell Observatory, “Near Earth Object Search,” 1 April 2008, http://asteroid.lowell.edu/asteroid/loneos/loneos.html
14 California Institute of Technology, “The Near Earth Object Wide-field Infrared Survey Explorer Science Data Center,” Infrared Processing and Analysis Center, 05 April 2016, http://neowise.ipac.caltech.edu/
15 B612 Foundation, “The Sentinel Mission,” Our Mission, 2015, https://b612foundation.org/our-mission/#sentinel-mission
16 Large Synoptic Survey Telescope, “The Large Synoptic Survey Telescope,” 2016, https://www.lsst.org/
17 Charles Q. Choi, “Chicxulub Asteroid Impact: The Dino-Killer that Scientists Laughed at,” Space, 07 February 2016, http://www.space.com/19681-dinosaur-killing-asteroid-chicxulub-crater.html
18 Ian Sample, “Scientists reveal the full power of the Chelyabinsk meteor explosion Science,” 07 November 2016, https://www.theguardian.com/science/2013/nov/06/chelyabinsk-meteor-russia
19 World Nuclear Association, “Hiroshima, Nagasaki, and Subsequent Weapons Testing,” March 2016, http://www.world-nuclear.org/information-library/safety-and-security/radiation-and-health/hiroshima,-nagasaki,-and-subsequent-weapons-testin.aspx
20 Peter Schulte et al, “The Chicxulub Asteroid Impact Mass Extinction at the Cretaceous-Paleogene Boundary,” Science, 05 March 2010, http://science.sciencemag.org/content/327/5970/1214.full
21 Shrrirup P. Nambiar et al, “Architecture for Mitigating Short-Term Warning Cosmic Threats: READI Project,” National Aeronautic and Space Administration, March 2016, https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160010365.pdf
22 National Research Council, “Defending Planet Earth: Near-Earth-Object surveys and hazard mitigation strategies,” 2010, https://www.nap.edu/catalog/12842/defending-planet-earth-near-earth-object-surveys-and-hazard-mitigation
23 Alaa Hussein et al, “From Detection to Deflection: Mitigation Techniques for Hidden Global Threats of Natural Space Objects with Short Warning Time,” Acta Astronautica, 07 June 2016, http://www.sciencedirect.com.cyber.usask.ca/science/article/pii/S009457651630306X
24 UCSB Experimental Cosmology Group, “Directed Energy Planetary Defense,” 2016, http://www.deepspace.ucsb.edu/projects/directed-energy-planetary-defense
25 Dennis Bonilla, “Kinetic Impactor,” National Aeronautic and Space Administration, 30 July 2015, http://www.nasa.gov/content/asteroid-grand-challenge/mitigate/kinetic-impactor
26 European Space Agency “Making history: 15000 NEAs and counting…”21 October 2016, http://neo.ssa.esa.int/news-archivep_p_id=62_INSTANCE_qyX7&p_p_lifecycle=0&p_p_state=normal&p_p_mode=view&p_p_col_id=column2&p_p_col_count=1&_62_INSTANCE_qyX7_struts_action=%2Fjournal_articles%2Fview&_62_INSTANCE_qyX7_groupId=10157&_62_INSTANCE_qyX7_articleId=23331&_62_INSTANCE_qyX7_version=1.3
27 National Aeronautics and Space Administration, “Why Infrared” NeoCam: Finding asteroids before they find us, http://neocam.ipac.caltech.edu/page/whyinfrared
28 National Aeronautics and Space Administration, “Near Earth Asteroid Tracking (NEAT),” Near Earth Object Program, 2016, http://neo.jpl.nasa.gov/programs/neat.html