Mission’s Impact
Mykaela Buhr, Dana Demmings, Charlotte Lalonde, Krista de Feijter, Jami Mcleod
Source: https://astronomytopicoftheday.wordpress.com/2015/10/23/close-pass-of-asteroid-2015-tb145-on-halloween-underscores-need-for-science/
Introduction
Asteroids have been the conversation to which is both fascinating and frightening to people on Earth. Some of the discussions have led to investigations of what they are, where they are located, how they become near-Earth asteroids (NEAs). Continuous development of missions and technologies not only allow us to gain a better understanding of how to avoid future collisions with Earth, but also gives critical new information that helps us understand more about the planet we live on. The importance of understanding asteroids lays with the significance of human life as we know it. Some of the topics that will be discussed are the basics of asteroids, NEAs, including how they become NEAs, and the process of detecting and tracking NEAs. Next, we will focus on the Dawn, Hayabusa, and the DART mission. These missions are the core of understanding and gaining insight into asteroids from Earth. How are current missions furthering our advancement of detecting NEAs and why are they important to humanity’s survival? Dawn, Hayabusa, and DART are current missions that are concentrating on detecting, observing, collecting and analyzing data while coming up with solutions to prevent a cataclysmic collision with the planet.
Asteroids
Figure 1 – The region between Jupiters and Mars is known as the main asteroid belt and contains the majority of asteroids. Source: https://www.eso.org/public/outreach/eduoff/cas/cas2003/cas-projects/uk_nt7_1/
Asteroids are objects in our solar systems that were formed 4.6 billion years ago, during the formation of our solar system.1Their composition includes rocks, metals and other elements such as hydrogen, oxygen or iron.2 Unlike most celestial bodies, asteroids are irregular in their shape and size.3Asteroids can range from 530 kilometers to less than 10 meters in diameter.4 The majority of asteroids lie within three regions of our solar system; the main asteroid belt, as Trojans to other planets, and as NEAs.2
Figure 2 – Jupiter’s Trojan asteroids are a large group of asteroids that lie ahead and behind the planets orbit. Jupiter is not the only planet that has Trojan asteroids in their neighbourhood. Mars, Neptune, Saturn and Earth all have NASA confirmed Trojan asteroids. Source: http://www.astronomy.com/magazine/news/2018/09/exploring-jupiters-trojan-asteroids
The main asteroid belt is located between Mars and Jupiter. As discussed by NASA, in the early years of our solar system the formation of Jupiter ended the creation of the planets, creating a region that causes small bodies to collide forming asteroids.1 In Jupiter’s early years within our solar system, it moved inwards and outwards from its current position.5 This slow, gradual movement affected different aspects of our solar system including the asteroid belt.5 As Jupiter moved towards its current location, it began deflecting icy objects towards the sun. Over time the objects lost their ice composition and became rocky substances that are a part of the asteroid belt.
Next, Trojan asteroids can be found orbiting in front (leading group) and behind (trailing group) of planets, such as Jupiter, Mars, Neptune, and even Earth.6 Currently, over 4,800 Trojan asteroids are orbiting in Jupiter’s neighbourhood.5 The gravitational pull between the sun and the planet they are orbiting create a balance for the asteroid’s orbit. 1 Finally, NEAs orbit closer to Earth than the Sun, rather than within the main asteroid belt..2
Near-Earth Asteroids
For asteroids to become NEAs, they need to be ejected from the main asteroid belt and orbit relatively close to Earth.1 Understanding NEAs is extremely important as their potential collision with Earth poses a danger to humanity. NEAs only survive in their orbits for 10 – 100 million years due to orbital decay, collisions with the inner planets, or ejection from the solar system.7 While NEAs are continually being eliminated they are also being replenished from the asteroid belt.7 There are three theories for how asteroids become NEA which includes, the Yarkovsky effect, Kazai Resonance, and gravitational pull.
The first explanation is the Yarkovsky effect, which demonstrates the impact the sun has on asteroids in the main asteroid belt.4 As asteroids orbit near the sun they are constantly heating up, and as a result, a force is created. The force has a gentle push on the asteroids, which over time can cause the asteroid to slowly drift outside of its original orbital pattern.4
Figure 3 – The Yarkovsky Effect explained. Source: https://www.asteroidmission.org/galleries/word-of-the-week/yarkovsky-effect/
The second explanation is the Kozai Resonance, which involves the orbital resonances of larger planets in our solar system.4 Orbital resonance happens when gravity pushes objects to orbit in specific patterns. When the two objects are not comparable in size, the resonance causes the larger object to eject the smaller object such as an asteroid.8
Finally, the gravitational pull of planets can affect an asteroids orbit. As Jupiter is the largest planet in our Solar System, its gravitational pull is the most intense, affecting every planet and celestial objects.9 The intense pull and close encounters with Mars can cause Jupiter to change the orbit of asteroids. Disrupted orbits can knock an asteroid out of the main belt and into space towards other planets, such as Earth. 1
Detection & Tracking
According to NASA, as of 2016, more than 15,000 NEAs are orbiting within 30 million miles of Earth’s orbit.10 Currently, there are no known asteroids that pose a threat of potential impact to Earth.10 However, it is essential to track and monitor asteroids over time. The first step in any mission regarding an asteroid begins with detecting and then monitoring its movement.
The process for most detection and tracking is by predicting NEAs orbits based on the initial observations and then to follow up when visible to telescopes. This allows observers to see how accurate their prediction was, even though it can be very time-consuming.10 Currently, Nasa has many discovery teams focused on detecting new NEAs by using CCD cameras.11 CCD images are taken within the same regions of the sky and then comparisons are done to determine any potential NEA.12 This initial observation allows other methods of detection and tracking to focus on particular NEAs. A few methods of detection and tracking include NEOWISE, ground-based telescopes, and amateur asteroid hobbyists.
Figure 4 – NEOWISE is a NASA funded project for asteroid-hunting. It is responsible for collecting data on orbits, size, composition, and the discovery of the first known Earth Trojan. Source: https://www.jpl.nasa.gov/spaceimages/details.php?id=pia17254
NEOWISE is an astrophysics spacecraft that has been recrafted to discover and characterize NEAs.10 It is an infrared telescope that can rapidly characterize NEAs while accurately measuring their dimensions.11 The main advantage NEOWISE has in comparison to ground-based observations is its sensitivity to light and dark colour objects.11 Another advantage against a ground-based telescope is its ability to observe infrared wavelengths. Infrared light from celestial objects in space is highly absorbed by Earth’s atmosphere.12 A ground-based telescopes needs to be located at a high altitude in a very dry climate, and it’s limited to near-infrared wavelength observations.12
with minor amounts of water, nitrogen oxide, neon, hydrogen-deuterium-oxygen, krypton, and xenon.
Ground-based telescopes perform follow up observations to help with orbit calculations while also studying the physical aspects of the objects.14 Amateur observers, such as Robert Holmes, also use ground-based telescopes to aid in studying NEAs.15 Holmes has four different telescopes he uses to observe asteroids, beginning his journey as a volunteer and now working full-time for NASA.15 Detection, observing and tracking asteroids is the backbone of NEA research and essential for the Dawn, Hayabusa, and DART missions.
Dawn Mission
Figure 5 – The Dawn spacecraft approaching Vesta. Source: https://www.jpl.nasa.gov/news/news.php?feature=4425
The Dawn mission is an extraordinary collaboration of many countries and the first to observe and collect data from two bodies, Vesta and Ceres, located within our Solar System’s main asteroid belt.16 The ability to compare Vesta and Ceres with the same instruments allow scientists to gain a deeper understanding of planetary origins and their evolutionary processes.17 The Dawn mission ion propulsion spacecraft was launched at dawn 200 years after Vesta was discovered.18 Dawn orbited Earth until it met up with Mars which provided a boost, called a gravity assist. The gravity assist allowed Dawn to reach Vesta where it reduced its orbit and spent time making observations. Dawn then left Vesta’s orbit and reached Ceres, where it continued to collect data.18 Observations were made at different orbits around the two asteroids called the survey orbit, the high altitude mapping orbit, and the low altitude mapping orbit.19 At these different heights around Vesta and Ceres, Dawn is tasked to acquire colour images, map geographic features and mineral composition, measure the gravitational field, and search for moons.18 The instruments aboard the spacecraft to make these observations are a camera, gamma-ray spectrometer, neutron spectrometer, visible mapping spectrometer, and an infrared mapping spectrometer. The gravity measurements are done by using a telecommunications subsystem and the Deep Space Network.20 Dawn has to pause it’s data finding while sending information back to Earth.21
Figure 5 – Dawn mission interplanetary trajectory. Source: https://www.jpl.nasa.gov/blog/2013/4/to-be-in-the-right-place-dawn-catches-up-with-time
One of the most pertinent discoveries of Dawn regarding NEAs from the data received has confirmed that howardite-eucrite-diogenite meteorites on Earth came from Vesta.22 Large impacts to Vesta, most notably at the southern region, caused pieces of the asteroid to be flung out into space and some of these meteorites struck the Earth.23 Vesta once had more water than expected and there may even be water in the sub-surface.18 Scientists now believe, through Dawn’s observations and other missions, that wet asteroids were the most likely source of water to Earth and the inner solar system.18 While the Dawn mission just came to a close on November 1, 2018, the data obtained will continue to be analyzed by scientists for many years and has already had a huge impact on what we know today about the Earth.
Hayabusa Mission
The Japanese spacecraft that participated in the Hayabusa mission brought back a sample of asteroid material to Earth in 2010 from a small NEA called 25143 Itokawa. It marks the second time in history that a spacecraft has landed on the surface of an asteroid.24 NASA’s Jet Propulsion Laboratory facilitated the Hayabusa mission by operating the spacecraft and monitoring ground communications through the Deep Space Network of antennas and provided the mission with navigators who worked closely with the Japanese navigation team to guide Hayabusa.25 The Mission was launched on May 9th, 2003 and Hayabusa touched down on the surface of the asteroid Itokawa in January 2007. Hayabusa flew around the asteroid surface from a distance of about 20 km away, which is known as the gate position. Once the spacecraft moved closer to the surface, known as the home position, it approached the asteroid for a series of soft landings at the safe site.26 The spacecraft spent several months surveying and collecting samples of the asteroid for further analysis.
Although the acceleration and force of the Hayabusa are considerably lower than traditional missions, the spacecraft used four ion engines that made it possible to land on the asteroid.27> During the time spent on the asteroid, the spacecraft used scientific instruments to collect the asteroid samples. The widespread camera and telescopic cameras were used to take detailed images, while X-ray spectrometers, near-infrared spectrometers, light detection and ranging, and the small rover MINVERA were used to study the asteroid’s surface.28 After sample collection, the spacecraft made its way back to Earth. On June 13th, 2010 the Hayabusa spacecraft discharged a 40-centimeter-wide capsule in Earth’s atmosphere. The capsule shot down to the Woomera Protected Area in South Australia, where ground teams retrieved it the next day.29 Thousands of particles were found in the sample containers. Many of these particles demonstrate that they are asteroid grains by their chemistry and mineralogy, but were also mixed with contaminant particles from the spacecraft.30 Nevertheless, these are the first explicit samples of an asteroid and their geological context established from extensive spacecraft surveys. These samples have great scientific value as they determine the particles that make up and asteroid. The material of the asteroid took several months to analyze. Scientists found minerals such as olivine and pyroxene, which are common on Earth and have been found on the Earth’s moon and Mars. The particles were only 10 micrometers in size. Many findings confirm that the dust on 25143 Itokawa was the same as the material on an LL chondrite type of meteorite. This finding confirms the connection between meteorites and asteroids.32 The Asteroid is currently 4.6 billion years old, which is the age of our solar system itself and is also held together by gravity. Itokawa occupied the main asteroid beltup until only the past two hundred thousand years. It now dwells in a different orbit as a NEA, which could result in a collision with Earth within the next million years.33 The success of the mission inspired a second mission with the spacecraft, called Hayabusa 2. The second asteroid sampling mission was launched in December 2014 and successfully landed on the asteroid 162173 Ryugu in July 2018.29
DART Mission
Figure 7 – Two different views of the DART spacecraft. The left view also shows the Radial Line Slots Array (RLSA) antenna with (solar arrays rolled up). The isometric view on the right shows a clearer view of the NEXT-C ion engine. Source: https://www.nasa.gov/planetarydefense/dart
NASA has determined that without a plan in place ahead of time, the use of a kinetic impactor device to deflect an asteroid could take 20 years to prepare.34 The Double Asteroid Redirection Test (DART) mission will be the first to use a spacecraft to change the trajectory of an asteroid using the kinetic impact approach.35 This first attempt at altering an asteroid’s course will help scientists to refine the process and could reduce the preparation time to 1-2 years.34 to launch between December 2020 and May 2021 the DART mission (a partnership between NASA and John Hopkins University’s Applied Physics Laboratory(APL)) will take advantage of new technology in propulsion, navigation, and photography all wrapped into the only instrument on board the DRACO.35 The target is Didymos B, part of a binary asteroid called Didymos, chosen because two reference points ensure more reliable tracking and the Didymos system is the size of a typical potentially hazardous asteroids (PHA).35
Figure 8 – Simulated image of the Didymos system. Source: https://www.nasa.gov/planetarydefense/dart
Navagation will be powered by NASA’s NEXT-C electric propulsion engine which ionizes xenon gas into a plasma which is accelerated through a magnetic field producing thrust for the spacecraft.35 The NEXT-C engine provides three times the power of previous NASA engines with lower operating costs, allowing spacecraft to stay in use longer.37 Navigation will be provided by the SMART Nav system designed by John Hopkins Universities APL.38 Nav will determine the best approach to the asteroid, the impact site, and make fine tune adjustments right up to the collision.38 Didymos Reconnaissance and Asteroid Camera for Op-nav (DRACO) will be the eyes of SMART Nav, providing the system with the necessary information to choose an impact site.38
Designed from the Long Range Reconnaissance Imager (LORRI), previously used by NASA to image Pluto,40 DRACO uses a signal/noise ratio to capture images that will be sent back to Earth at an ideal rate of one image every 5 seconds.39 These images will be compared to Earth-based observations after the impact, made possible by Didymos’ proximity.39 DRACO makes less noise than LORRI did, allowing for higher sensitivity as well as using a complementary metal-oxide-semiconductor (CMOS) detector which will produce low saturation images.39 Starting four hours before impact the DRACO camera will be capable of distinguishing Didymos A and B, leaving a small period of time to make navigation adjustments and collect images.39 The DART mission will provide scientists with the information needed to develop a working plan to defend the Earth in the case of an asteroid on a collision course with the planet as well as providing insight into the composition of asteroids.
Conclusion
The objective of our research was to determine how current missions and projects are furthering our understanding of detecting NEAs, which is important to humanity’s survival. Through our research we have found that NEAs need to be ejected from the main asteroid belt so that they can begin orbiting close to Earth. Some of the explanations for NEAs are the Yarkovsky effect, the Kazai Resonance, and gravitational pull. This leads us to the benefits of detection and tracking. Some of the methods used are telescopes, CCD Cameras, NEOWISE and ground-based telescope. All of these contributed to our understanding of asteroids and have significant importance to each of the missions. Dawn Mission revolutionised space research by orbiting two of the largest objects in our Solar System’s main asteroid belt, a feat that had never been managed before. The observations made on Vesta and Ceres have helped scientists discover that a large majority of our Earth’s water may have come from water rich asteroids at the dawn of our solar system. The Hayabusa Mission was a Japanese spacecraft that brought back a sample of asteroid material for the second time in our history. As a result of this mission scientists were able to identify some of the samples that were collected, which confirms the connection between asteroids and meteorites. The DART mission will pioneer how spacecrafts change the trajectory of asteroids by using the kinetic impact approach. It will be able to provide information needed to determine how to prevent a future collision with Earth, including providing the necessary information to understand the composition of asteroids. Throughout our research the Dawn, Hayabusa, and DART missions concentrated on detecting, observing, collecting and analysing data while coming up with solutions to prevent a cataclysmic collision with the planet.
Understanding asteroids and NEAs; and the importance of detection and tracking is essential in protecting our world against future asteroid collisions. Each mission furthers our knowledge of NEAs and advances our defences
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