令人驚訝的小行星樣本顯示Bennu可能起源於海洋世界 (1/2)

Recently CNN news on-line reported the following:

Surprising asteroid sample reveals Bennu may have originated from an ocean world (1/2)

By Ashley Strickland, CNN

 4 minute read

Updated 3:45 PM EDT, Thu June 27, 2024

CNN— An early analysis of a sample collected from the asteroid Bennu suggests that the space rock had an unexpectedly water-rich past — and it may have even splintered off from an ancient ocean world.

The NASA OSIRIS-REx mission scooped up the 4.3-ounce (121.6-gram) pristine sample from the near-Earth asteroid in 2020 and returned it to Earth last September.

Since then, scientists have been analyzing the asteroid’s rocks and dust to see what secrets they may contain about the asteroid’s composition and whether it could have delivered the elements for life to Earth. Asteroids also intrigue scientists because they are the leftover remnants from the formation of the solar system.

An initial review of some of the sample, shared in October, suggested that the asteroid contained a large amount of carbon.

During a new analysis of the sample, the team discovered that Bennu’s dust is rich in carbon, nitrogen and organic compounds, all of which helped form the solar system. These ingredients are also essential to life as we understand it and could help scientists better understand how Earth-like planets evolve.

A study detailing the findings appeared Wednesday in the journal Meteoritics & Planetary Science.

“OSIRIS-REx gave us exactly what we hoped: a large pristine asteroid sample rich in nitrogen and carbon from a formerly wet world,” said study coauthor Jason Dworkin, OSIRIS-REx project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, in a statement.

The elements for life

The biggest surprise was finding magnesium-sodium phosphate within the sample, which remote sensing didn’t initially detect when OSIRIS-REx, or the Origins, Spectral Interpretation, Resource Identification, and Security — Regolith Explorer mission, was orbiting Bennu.

Magnesium-sodium phosphate is a compound that can be dissolved in water and serves as a component of biochemistry for life.

It’s possible that the asteroid may have broken away from a tiny, primitive ocean world that no longer exists in our solar system, the researchers said.

The asteroid’s sample largely consists of clay minerals, including serpentine, which makes the sample remarkably similar to rocks found at midocean ridges on Earth. These ridges are where material from the mantle, the layer beneath Earth’s surface crust, encounters water.

A similar phosphate was found in a sample from the asteroid Ryugu collected by the Japan Aerospace Exploration Agency’s Hayabusa2 mission and returned to Earth in December 2020. But the compound from the Bennu sample is purer and has larger grains.

“The presence and state of phosphates, along with other elements and compounds on Bennu, suggest a watery past for the asteroid,” said co-lead study author Dante Lauretta, principal investigator for OSIRIS-REx and regents professor at the University of Arizona, Tucson, in a statement. “Bennu potentially could have once been part of a wetter world. Although, this hypothesis requires further investigation.”

(to be continued)

Translation

CNN - 對從小行星 Bennu 收集的樣本進行的早期分析表明，這顆太空岩石的過去出乎意料地含有大量水份 - 它甚至可能是從一個古老的海洋世界分裂出來的。

NASA 的 OSIRIS-REx 任務於 2020 年從接近地球小行星上挖出了 4.3 盎司（121.6 克）的原始樣本，並於去年 9 月將其帶回地球。

從那時起，科學家一直在分析這顆小行星的岩石和塵埃，看看它們可能包含有關小行星成分的秘密，以及它是否可以將生命所需的元素輸送到地球。小行星也引起了科學家的興趣，因為它們是太陽系形成過程中留下的殘餘物。

已在十月分享對一些樣本的初步審查表明，這顆小行星含有大量碳。

在對樣本的新分析中，研究小組發現 Bennu 的塵埃含大量碳、氮和有機化合物，所有這些都有助於形成太陽系。，這些成分對於我們所知的生命也是至關重要的，可以幫助科學家更好地了解像地球的行星是如何演化的。

週三，一項詳細介紹這項發現的研究在《隕石與行星科學》雜誌上發表。

研究合著者 Jason Dworkin 是位於馬利蘭州 Greenbelt 的美國宇航局 Goddard太空飛行中心的 OSIRIS-REx 計劃科學家，他說：「OSIRIS-REx 為我們提供了我們所希望的東西：來自以前潮濕世界的富含氮和碳的大型原始小行星樣本」。

生命的要素

最大的驚喜是在樣本中發現了磷酸鎂鈉，而當 OSIRIS-Rex 即是 Origins, Spectral Interpretation, Resource Identification, and Security — Regolith Explorer 繞著 Bennu 運行時，最初遙感應器並未檢測到這種物質。

磷酸鎂鈉是一種可溶於水的化合物，是生命生物化學的組成部分。

研究人員表示，這顆小行星可能是從太陽系中已經不再存在的微小原始海洋世界中脫離出來。

這顆小行星的樣本主要由黏土礦物組成，包括蛇紋石，這使得樣本與地球上在 “海洋中脊”所發現的岩石非常相似。這些山脊是來自地球地幔 (地殼以下的一層）的物質與水相遇的地方。

類似的磷酸鹽也在日本宇宙航空研究開發機構的 Hayabusa 2 號任中務所收集到, 之後於 2020 年 12 月送返回地球的小行星 Ryugu 樣本中發現。但 Bennu 樣本中的化合物較純淨，顆粒較大。

該研究的共同領導者、OSIRIS-REx 首席研究員、Tucson 亞利桑那大學攝政教授 Dante Lauretta 在一聲明中說: 「Bennu 上的磷酸鹽的存在和狀態，以及其他元素和化合物，表明這顆小行星的過去曾經有過水份」; 「Bennu 可能曾經是一個濕潤世界的一部分。不過，這一假設還需要進一步調查」。

（待續）

Note:

1. An asteroid (小行星) is a minor planet that orbit within the inner Solar System. They are rocky, metallic, or icy bodies with no atmosphere. The size and shape of asteroids vary significantly, ranging from small rubble piles under a kilometer to a dwarf planet almost 1000 km in diameter. (Wikipedia)

2. Mid-ocean ridges (海洋中脊) are geologically important because they occur along the kind of plate boundary where new ocean floor is created as the plates spread apart. The mid-ocean ridge is also known as a "spreading center" or a "divergent plate boundary." The plates spread apart at rates of 1 cm to 20 cm per year. (https://www.google.com/search?q=midocean+ridges+on+Earth&rlz=1C1CHBF_enCA985CA985&oq=midocean+ridges+on+Earth&gs)

3. The title Regents Professor serves as recognition of the highest academic merit and is awarded to faculty members who have made a unique contribution to the quality of the University through distinguished accomplishments in teaching scholarship, research, or creative work.