Peta baru yang luar biasa dari jiwa asteroid mengungkapkan dunia kuno logam dan batu

Para astronom di MIT dan di tempat lain telah memetakan komposisi asteroid Psyche, mengungkapkan permukaan logam, pasir, dan batu. Kredit: tangkapan layar dari NASA

Permukaan asteroid yang bervariasi Psyche menunjukkan sejarah yang dinamis, yang dapat mencakup letusan mineral, efek guncangan asteroid, dan mantel berbatu yang hilang.

Akhir tahun iniDan[{” attribute=””>NASA is set to launch a probe the size of a tennis court to the asteroid belt, a region between the orbits of Mars and Jupiter where remnants of the early solar system orbit the sun. Once within the asteroid belt, the spacecraft will zero in on Psyche, a large, metal-rich asteroid that is thought to be the ancient core of an early planet. The probe, named after its asteroid target, will then spend close to two years orbiting and analyzing Psyche’s surface for clues to how early planetary bodies evolved.

Ahead of the mission, which is led by principal investigator Lindy Elkins-Tanton ’87, SM ’87, PhD ’02, planetary scientists at MIT and elsewhere have now provided a sneak peek of what the Psyche spacecraft might see when it reaches its destination.

In a paper published on June 15, 2022, in the Journal of Geophysical Research: Planets, the planetary science team presents the most detailed maps of the asteroid’s surface properties to date, based on observations taken by a large array of ground telescopes in northern Chile. The maps reveal vast metal-rich regions sweeping across the asteroid’s surface, along with a large depression that appears to have a different surface texture between the interior and its rim; this difference could reflect a crater filled with finer sand and rimmed with rockier materials.

This illustration, updated in April 2022, depicts NASA’s Psyche spacecraft. Set to launch in August 2022, the Psyche mission will explore a metal-rich asteroid of the same name that lies in the main asteroid belt between Mars and Jupiter. The spacecraft will arrive in early 2026 and orbit the asteroid – also shown in this illustration – for nearly two years to investigate its composition. Credit: NASA/JPL-Caltech/ASU

Overall, Psyche’s surface was found to be surprisingly varied in its properties.

The new maps hint at the asteroid’s history. Its rocky regions could be vestiges of an ancient mantle — similar in composition to the rocky outermost layer of Earth, Mars, and the asteroid Vesta — or the imprint of past impacts by space rocks. Finally, craters that contain metallic material support the idea proposed by previous studies that the asteroid may have experienced early eruptions of metallic lava as its ancient core cooled.

“Psyche’s surface is very heterogeneous,” says lead author Saverio Cambioni, the Crosby Distinguished Postdoctoral Fellow in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “It’s an evolved surface, and these maps confirm that metal-rich asteroids are interesting, enigmatic worlds. It’s another reason to look forward to the Psyche mission going to the asteroid.”

Cambioni’s co-authors are Katherine de Kleer, assistant professor of planetary science and astronomy at Caltech, and Michael Shepard, professor of environmental, geographical, and geological sciences at Bloomsburg University.

Telescope Power

The surface of Psyche has been a focus of numerous previous mapping efforts. Researchers have observed the asteroid using various telescopes to measure light emitted from the asteroid at infrared wavelengths, which carry information about Psyche’s surface composition. However, these studies could not spatially resolve variations in composition over the surface.

Cambioni and his colleagues instead were able to see Psyche in finer detail, at a resolution of about 20 miles per pixel, using the combined power of the 66 radio antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile. Each antenna of ALMA measures light emitted from an object at millimeter wavelengths, within a range that is sensitive to temperature and certain electrical properties of surface materials.

“The signals of the ALMA antennas can be combined into a synthetic signal that’s equivalent to a telescope with a diameter of 16 kilometers (10 miles),” de Kleer says. “The larger the telescope, the higher the resolution.”

On June 19, 2019, ALMA focused its entire array on Psyche as it orbited and rotated within the asteroid belt. De Kleer collected data during this period and converted it into a map of thermal emissions across the asteroid’s surface, which the team reported in a 2021 study. Those same data were used by Shepard to produce the most recent high-resolution 3D shape model of Psyche, also published in 2021.

Di sebelah kiri, peta ini menunjukkan karakteristik permukaan di Psyche, dari area berpasir (ungu/rendah) hingga berbatu (kuning/tinggi). Peta di sebelah kanan menunjukkan kelimpahan mineral di Psyche, dari rendah (ungu) hingga tinggi (kuning).

untuk mengejar pertandingan

Dalam studi baru, Cambioni menjalankan simulasi Psyche untuk mengetahui sifat permukaan mana yang paling cocok dan menjelaskan emisi panas yang diukur. Dalam masing-masing dari ratusan skenario simulasi, ia memetakan permukaan asteroid dengan kombinasi material yang berbeda, seperti daerah dengan kelimpahan mineral yang berbeda. Dia memodelkan rotasi asteroid dan mengukur bagaimana bahan simulasi pada asteroid akan memancarkan emisi panas. Campione kemudian mencari emisi simulasi yang paling cocok dengan emisi aktual yang diukur oleh ALMA. Skenario ini, menurutnya, akan mengungkapkan peta material permukaan asteroid yang paling mungkin.

“Kami menjalankan simulasi ini wilayah demi wilayah sampai kami dapat mengidentifikasi perbedaan sifat permukaan,” kata Campione.

Studi ini menghasilkan peta rinci sifat permukaan Psyche, menunjukkan bahwa antarmuka asteroid kemungkinan ditutupi dengan berbagai macam bahan. Para peneliti menekankan bahwa permukaan Psyche secara umum kaya akan mineral, tetapi kelimpahan mineral dan silikat bervariasi tergantung pada permukaannya. Ini mungkin petunjuk tambahan bahwa asteroid, pada awal pembentukannya, mungkin memiliki mantel kaya silikat yang telah menghilang.

Mereka juga menemukan bahwa saat asteroid mengorbit, material di dasar depresi besar – kemungkinan kawah – mengubah suhu jauh lebih cepat daripada material di sepanjang tepinya. Ini menunjukkan bahwa dasar kawah ditutupi dengan “kolam” material berbutir halus, seperti pasir di tanah, yang memanas dengan cepat, sedangkan tepi kawah terdiri dari material berbatu yang lebih lambat dan lebih hangat.

“Kolam material berbutir halus telah terlihat di asteroid kecil, gravitasinya cukup rendah untuk guncangan permukaan yang menyebabkan material yang lebih halus berkumpul,” kata Campione. “Tapi Psyche adalah tubuh yang besar, jadi jika bahan berbutir halus terakumulasi di bagian bawah depresi, itu agak menarik dan misterius.”

“Data ini menunjukkan bahwa permukaan Psyche heterogen, dengan perbedaan komposisi yang mencolok,” kata Simone Marchi, seorang ilmuwan di Southwest Research Institute dan penyelidik misi NASA Psyche, yang tidak terlibat dalam penelitian ini. “Salah satu tujuan utama misi Psyche adalah untuk mempelajari komposisi permukaan asteroid menggunakan sinar gamma, spektrometer neutron, dan pencitraan warna. Jadi, potensi keberadaan gen komposisi adalah sesuatu yang ingin dipelajari lebih lanjut oleh tim psikologi.”

Referensi: “Permukaan Heterogen Asteroid (16) Jiwa” oleh Saverio Campione, Catherine de Clare dan Michael Shepherd, 19 Mei 2022, Tersedia di sini. Jurnal Penelitian Geofisika: Planet.
DOI: 10.1029/2021JE007091

Penelitian ini didukung oleh EAPS Crosby Distinguished Postdoctoral Fellowship, dan sebagian oleh Yayasan Heising-Simons.