{"id":26225,"date":"2021-11-18T11:29:09","date_gmt":"2021-11-18T11:29:09","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/?post_type=purple_issue&p=26225"},"modified":"2021-11-18T11:29:09","modified_gmt":"2021-11-18T11:29:09","slug":"dart-a-mission-with-impact","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/2021\/11\/18\/dart-a-mission-with-impact\/","title":{"rendered":"DART: A mission with impact"},"content":{"rendered":"\n

Govert Schilling takes a look at the NASA mission that will attempt to deflect an asteroid, part of a collaboration with ESA that could save Earth from a catastrophic impact<\/p>\n\n

\"\"
Launching this winter, when the DART mission is intentionally crashed into the space rock Dimorphos it will test humanity\u2019s ability to alter asteroid orbits and avert a collision with Earth <\/figcaption><\/figure><\/div>\n\n

Over its four and a half billion year lifetime, Earth has been battered and pummelled by cosmic collisions. Some 50,000 years ago, a small asteroid slammed into northern Arizona, leaving a 1,200m-wide impact crater and turning the area into a wasteland. A similar impact today would have catastrophic consequences \u2013 unless we could find a way to divert the space rock. Next year, NASA will test the technology to do just that, by firing a halftonne spacecraft into a small asteroid in an attempt to deflect its path.<\/p>\n\n

During a launch window that stretches from 24 November to 15 February, a SpaceX Falcon 9 rocket will send the DART (Double Asteroid Redirection Test) spacecraft on a collision course with the small moon of asteroid 65803 Didymos. In late September or early October 2022, DART will smash into the 160m-diameter object, giving it a decent kick. Telescopes on Earth will measure the resulting change in the moonlet\u2019s orbit, while the European Space Agency\u2019s (ESA\u2019s) Hera mission will study the damaged target up close in 2026. <\/p>\n\n

\"\"
With a diameter of 1,200km, Meteor Crater in Arizona, USA was caused by the impact of a meteor 50m across some 50,000 years ago. A bus parked nearby is circled for scale <\/figcaption><\/figure><\/div>\n\n

Ever since the discovery of 433 Eros in 1898 \u2013 the first asteroid known to cross the orbit of Mars \u2013 astronomers have realised that Earth is at risk from cosmic impacts. Today, they know of over 2,200 \u2018potentially hazardous asteroids\u2019 (PHAs): objects larger than 140m in diameter that can approach our planet to within 7.5 million kilometres. Smaller ones are even more numerous. Tiny space rocks, just 10m or 20m wide, are regularly seen passing within the Moon\u2019s orbit, or exploding in the atmosphere, like the Chelyabinsk impactor in February 2013.<\/p>\n\n

While the Chelyabinsk blast did not claim any lives, a 100m-wide asteroid could destroy a large city. Objects that size collide with Earth once every 5,000 years or so, on average. Increasing the diameter to 400m brings the impact frequency down to once every 100,000 years, but the damage is proportionally larger and could wipe out an area the size of France.<\/p>\n\n

\u201cWe need to find those objects before they find us,\u201d says Kelly Fast, director of NASA\u2019s Planetary Defense Coordination Office.<\/p>\n\n

Making an impact<\/strong><\/h5>\n\n

Searching for and finding an asteroid is one thing, but doing something about it is another. And while astronomers are constantly discovering new NEOs (near-Earth objects), there is no single existing programme for defusing an approaching cosmic missile. Scientists don\u2019t even know what the best strategy would be, although the \u2018kinetic impactor\u2019 technique \u2013 basically, kicking the oncoming rock out of the way \u2013 appears to be a relatively simple, effective and cheap solution. Except that no one has ever tried it.<\/p>\n\n

With DART, that\u2019s going to change. Next year, the 360kg spacecraft, about the size of a golf cart, will deliberately crash itself into a small asteroid at a velocity of 6.6km\/s. DART is a very basic spacecraft, developed and built by the Johns Hopkins Applied Physics Laboratory, and fitted out with little more than an ion engine, a few small thrusters, five Sun sensors and a star tracker, simple radio antennas for communicating with Earth and a camera.<\/span><\/p>\n\n

\"\"
In 2013, an 8m-diameter hole in the ice of Russia\u2019s Lake Chebarkul was thought to have been caused by a fragment of the Chelyabinsk meteor<\/figcaption><\/figure><\/div>\n\n
\"\"
The intention of the DART impact is to alter the orbit that the moon Dimorphos takes around asteroid Didymos. The event will be witnessed by the LICIACube satellite<\/figcaption><\/figure><\/div>\n\n

Power will be provided by two roll-out solar arrays, each measuring 8.6m x 2.3m. And all of this will be intentionally destroyed less than a year from now, when DART slams into its target.<\/p>\n\n

That target is known as Dimorphos and it measures approximately 160m across. It\u2019s in orbit around asteroid Didymos (Greek for \u2018twins\u2019), which is almost five times larger, at 780m in diameter. Didymos is a typical near- Earth asteroid, discovered in 1996 by the Spacewatch project at Kitt Peak National Observatory in Tucson, Arizona. It rotates every 2.26 hours, and its elliptical orbit of the Sun takes it from the main asteroid belt to just outside Earth\u2019s orbit and back every 2.11 years.<\/span><\/p>\n\n

Astronomers discovered Dimorphos in 2003. This small moon of Didymos orbits the main asteroid every 11.9 hours at a distance of just 1.2km, moving at a leisurely pace of some 0.2m\/s \u2013 comparable to the walking speed of a tortoise. The destructive impact of the DART spacecraft will change this velocity by less than a millimetre per second (after all, hitting a 5 billion kilogram asteroid with a 500kg spacecraft is like throwing a peppercorn at the tortoise), but this should change the moon\u2019s orbital period by about 10 minutes \u2013 enough to be measurable from Earth.<\/span><\/p>\n\n

Anticipating reactions<\/strong><\/h5>\n\n

The truth is, however, that nobody really knows exactly what will happen.<\/p>\n\n

\u201cIt all very much depends on the internal structure of the target,\u201d explains Fast. A solid body will respond differently from a relatively loose \u2018rubble pile\u2019. Didymos may indeed resemble the rubblepile asteroids Bennu and Ryugu, which have recently been studied in detail by NASA\u2019s OSIRIS- REx spacecraft and the Japanese Hayabusa 2, respectively, but Dimorphos probably has more internal strength. Only time will tell.<\/span><\/p>\n\n

\"\"<\/figure><\/div>\n\n

\u201cIt\u2019s the very first time we\u2019re doing this,\u201d says Patrick Michel of the C\u00f4te d\u2019Azur Observatory in France, who is the principal investigator for ESA\u2019s Hera mission. \u201cWe simply have no idea about the result.\u201d<\/p>\n\n

At the time of impact, Didymos will be some 11 million kilometres from Earth, so there won\u2019t be anything to see from the ground. To witness the collision from up close, NASA has selected the Italian firm Argotec in Turin to develop a small \u2018CubeSat\u2019 that will be released by DART just prior to its arrival. LICIACube, as the tiny satellite is called (Light Italian CubeSat for Imaging of Asteroids), is equipped with a camera that will relay pictures of the impact back to Earth.<\/span><\/p>\n\n

An inside story<\/strong><\/h5>\n\n

Of course, LICIACube will have about the same relative velocity to Didymos and Dimorphos as DART has, around 6.6km\/s, so it will shoot past and be unable to study the aftermath of the collision in detail. That will be the task of the Hera mission, due to be launched in October 2024. Hera is going to rendezvous with Didymos in 2026; its observations of the crater produced by DART will tell scientists a lot about the internal structure and composition of the small asteroid moon, says Michel. To that end, the Hera mission will be fitted with optical and infrared cameras, a laser rangefinder and a hyperspectral imager. In addition, Hera may also carry two small CubeSats, as well as a tiny lander and impactor built by JAXA, the Japanese space agency.<\/span><\/p>\n\n

\"\"
A larger asteroid like Bennu \u2013 as imaged here by the OSIRIS-REx spacecraft \u2013 may be a target for HAMMER, a larger \u2018kinetic impactor\u2019 which is under development<\/figcaption><\/figure><\/div>\n\n

Of course, the real question is: will the experience and information gained by DART and Hera enable us to successfully ward off a potentially catastrophic asteroid impact in the future? That all depends on the particulars of such an event, says Amy Mainzer, a University of Arizona planetary researcher who is the project scientist for NEOWISE, NASA\u2019s spacebased asteroid hunter. Suppose a near-Earth asteroid is detected tomorrow that is going to impact Earth in 2070. That gives us enough warning time: a tiny change of velocity now will be enough to change its course, so that by the time it crosses Earth\u2019s orbit in 50 years our planet will no longer be in its way.<\/span> 25 September 2135. Alternatively, it could be \u201cWe don\u2019t want to discover these objects a few days before they are going to hit us, but instead many years or decades in advance,\u201d says Mainzer.<\/span><\/p>\n\n

HAMMER time<\/strong><\/h5>\n\n

Even then, a DART-like impact won\u2019t be enough to veer a much larger asteroid off course. That\u2019s why technicians at Lawrence Livermore National Laboratory have designed a much more powerful \u2018kinetic impactor\u2019, called HAMMER (Hypervelocity Asteroid Mitigation Mission for Emergency Response). Measuring 9m in length and weighing almost 9 tonnes, with enough warning time HAMMER could successfully deflect a 500m-diameter object like Bennu \u2013 the asteroid studied by OSIRIS-REx, which has a minute chance of impacting Earth on 25 September 2135. Alternatively, it could be used to kick a 30m-object out of the way if it was discovered only weeks before impact.<\/span><\/p>\n\n

\"\"
When the powerful Vera C Rubin Observatory, with its innovative three-mirror design, becomes fully operational, it is very likely to spot more potentially hazardous space rocks heading towards Earth<\/figcaption><\/figure><\/div>\n\n

As far as planetary defence is concerned, discovery and mitigation are two sides of the same coin. The NASA office run by Fast is coordinating all US activities in this field, she explains, with a budget of about $150m per year. Moreover, the United Nations Committee On the Peaceful Uses of Outer Space (COPUOS) has installed two working groups to foster international collaboration: the Asteroid Warning Network and the Space Mission Planning Advisory Group. After all, threatening asteroids don\u2019t care too much about borders and nationalities, and a large impact would have global consequences.<\/span><\/p>\n\n

At present, astronomers don\u2019t know of any sizeable asteroid that will hit us in the next couple of centuries. But most of the estimated 15,000 or so potentially hazardous objects (the ones larger than 140m) are still undiscovered, and 50m-diameter space rocks are much more numerous still. When the Vera C Rubin Observatory in Chile comes online in late 2023, the number of new asteroid discoveries is going to explode, and it\u2019s likely it will spot one heading towards us before too long. By then, we will be grateful for the rehearsal opportunity that the DART mission offers.<\/p>\n\n

The recent COVID-19 pandemic and the upcoming climate crisis have taught us that humankind is not particularly good at preparing for global catastrophes before they happen. In the case of cosmic impacts, the DART mission is at least a first step in finding out what can be done, so we are prepared to take charge and avert disaster when the need arises.<\/p>\n\n

<\/div>
\n

Lucy and the Trojans<\/h4>\n\n\n\n

The mission will increase our knowledge of the asteroid swarms orbiting with Jupiter<\/strong><\/p>\n\n\n\n

\"\"
The Lucy mission is due to visit the Trojan asteroids in 2027. Each one is named after a mythical figure from the Trojan War<\/figcaption><\/figure><\/div>\n\n\n\n

By the time you\u2019re reading this story, NASA\u2019s Lucy mission should be on its way to study the Trojan asteroids, having launched in October 2021. Trojans are asteroids that share Jupiter\u2019s orbit around the Sun, either 60\u00b0 ahead or 60\u00b0 behind the giant planet. There\u2019s thought to be at least a million of them larger than 1km in diameter.<\/span><\/p>\n\n\n\n

Launched on an Atlas V rocket, Lucy will perform gravity assist flybys with Earth in 2022 and 2023 to gain speed. In 2025, it will fly by the main belt asteroid 55246 Donaldjohanson, named after the paleoanthropologist who discovered the \u2018Lucy\u2019 hominin fossil after which the mission has been<\/span> named. In 2027, Lucy will arrive in the \u2018leading\u2019 cloud of Trojans, studying four of them in detail.<\/p>\n\n\n\n

Next, a third gravity assist with our home planet in 2031 will send the spacecraft to the trailing cloud, where it will orbit the secondlargest Trojan, 617 Patroclus (140km in diameter), which is accompanied by a smaller companion body known as Menoetius.<\/p>\n\n\n\n

Lucy\u2019s visual imager, nearinfrared imaging and thermal infrared spectrometers will study the composition and surface characteristics of these dark, puzzling objects, shedding light on their origin and, thus, on the early evolution of our Solar System.<\/p>\n<\/div><\/section>\n\n

Psyche, the mission to the heavy metal asteroid<\/h4>\n\n

Its target is a resource-rich metallic body, one of the most massive of its type<\/strong><\/p>\n\n

\"\"
NASA\u2019s Psyche mission will shed light on the violent collisions that shaped Earth and the other planets<\/figcaption><\/figure><\/div>\n\n

Like Lucy, Psyche is a NASA Discovery-class mission to learn more about asteroids. Psyche will focus on only one: a 220kmdiameter chunk of mostly iron and nickel, discovered in 1852, and bearing the same name.<\/p>\n\n

16 Psyche is one of the 10 most massive known asteroids, due to its metal content \u2013 the surface is around 90 per cent metal. Most planetary researchers believe that Psyche is the exposed metallic core of a protoplanet that lost its silicate mantle in a collision with another asteroid, probably billions of years ago. If they\u2019re right, then the mission will offer a unique way to look at the interior of a Solar System body usually hidden inside a planet\u2019s core.<\/span><\/p>\n\n

The launch of the Psyche spacecraft is scheduled for August 2022, on a Falcon Heavy rocket. In 2023, a close encounter with Mars will give the craft enough speed to reach its destination in early 2026.<\/span> Using solar electric propulsion (just like DART and Lucy), Psyche will enter orbit around the unusual metallic asteroid, to study its properties and elemental composition with a multispectral imager, a magnetometer and a gamma-ray spectrometer.<\/p>\n\n

<\/p>\n\n

\n\n
\n
\n
\"\"<\/figure><\/div>\n<\/div>\n\n\n\n
\n

Govert Schilling <\/strong>is an astronomy journalist and broadcaster, and author of Ripples in Spacetime. <\/em>The asteroid 10986 Govert is named after him<\/p>\n<\/div>\n<\/div>\n\n

<\/p>\n\n

PHOTOS: ILLUSTRATION NASA\/JOHNS HOPKINS APL, IFRPILOT\/ISTOCK\/GETTY IMAGES, NEWSCOM\/ALAMY STOCK PHOTO, NASA\/JOHNS HOPKINS APL, NASA\/JPL-CALTECH, NASA\/JOHNS HOPKINS APL, NASA\/GODDARD\/UNIVERSITY OF ARIZONA, RUBIN OBS\/NSF\/AURA, NASA\/JPL-CALTECH\/ASU, NASA\/JPL-CALTECH\/ARIZONA STATE UNIV.\/SPACE SYSTEMS LORAL\/PETER RUBIN<\/p>\n","protected":false},"excerpt":{"rendered":"

Govert Schilling takes a look at the NASA mission that will attempt to deflect an asteroid, part of a collaboration with ESA that could save Earth from a catastrophic impact<\/p>\n","protected":false},"author":24,"featured_media":26217,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ub_ctt_via":"","purple_page_number":"68","purple_custom_meta_purple_page_number":"68","purple_seq_number":"1","purple_custom_meta_purple_seq_number":"1","purple_source_article":"article_68-1.xml","purple_custom_meta_purple_source_article":"article_68-1.xml","purple_source_issue":"December-2021","purple_custom_meta_purple_source_issue":"December-2021","purple_external_id":"December-2021-68-1","purple_custom_meta_purple_external_id":"December-2021-68-1","purple_issue_code":"|0000086547||","purple_custom_meta_purple_issue_code":"|0000086547||","purple_android_product":"com.im.skyatnight.199","purple_custom_meta_purple_android_product":"com.im.skyatnight.199","purple_ios_product":"com.im.skyatnight.199","purple_custom_meta_purple_ios_product":"com.im.skyatnight.199","purple_web_product":"","purple_custom_meta_purple_web_product":"","purple_publication_id":"075fab74-0a21-4201-866a-899d6c41c40c","purple_migrated":"","kt_blocks_editor_width":""},"categories":[21],"tags":[14],"featured_image_src":"https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/11\/3de23fc9-7f5f-4bfe-91d8-cf0c09438678.jpg","author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"acf":{"readingTimeMinutes":"12","apple_news_title":""},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/11\/3de23fc9-7f5f-4bfe-91d8-cf0c09438678.jpg",2048,1448,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/11\/3de23fc9-7f5f-4bfe-91d8-cf0c09438678-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/11\/3de23fc9-7f5f-4bfe-91d8-cf0c09438678-300x212.jpg",300,212,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/11\/3de23fc9-7f5f-4bfe-91d8-cf0c09438678-768x543.jpg",768,543,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/11\/3de23fc9-7f5f-4bfe-91d8-cf0c09438678-1024x724.jpg",800,566,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/11\/3de23fc9-7f5f-4bfe-91d8-cf0c09438678-1536x1086.jpg",1536,1086,true],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2021\/11\/3de23fc9-7f5f-4bfe-91d8-cf0c09438678.jpg",2048,1448,false]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"Govert Schilling takes a look at the NASA mission that will attempt to deflect an asteroid, part of a collaboration with ESA that could save Earth from a catastrophic impact","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/26225"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/users\/24"}],"replies":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/comments?post=26225"}],"version-history":[{"count":9,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/26225\/revisions"}],"predecessor-version":[{"id":26761,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/posts\/26225\/revisions\/26761"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media\/26217"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=26225"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=26225"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/tags?post=26225"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}