NASA vil have din hjælp til at designe en stjerneskærm til at observere exoplaneter

Området for exoplanetstudier er nået langt i de seneste årtier. Til dato er 5.063 exoplaneter blevet bekræftet i 3.794 systemer ud over vores eget, med yderligere 8.819 kandidater, der venter på bekræftelse. I de kommende år forventes titusindvis af flere planeter at blive fundet takket være næste generations observatorier. Det ultimative mål i denne søgning er at finde planeter, der er "jordlignende", hvilket betyder, at de har en god chance for at understøtte liv. Dette er ingen nem opgave, da klippeplaneter, der er placeret inden for deres moderstjernes beboelige zoner (HZ'er), har en tendens til at kredse tæt, hvilket gør dem sværere at se.

For at gøre denne proces lettere, designer NASA et hybridobservatorium bestående af en "stjerneskygge", der vil blokere en stjernes lys, så et jordbaseret teleskop direkte kan afbilde planeter, der kredser om den. Konceptet er kendt som Hybrid Observatory for Earth-like Exoplanets (HOEE), og NASA leder efter offentligt input for at gøre det til virkelighed. Til det formål har de lanceret Ultralight Starshade Structural Design Challenge, hvor deltagerne bliver bedt om at udvikle et design til en letvægtsstjerneskyggestruktur, der kunne bruges som en del af HOEE-konceptet.

Udfordringen er hostet af GrabCAD, en Massachusetts-baseret startup, der er vært for en gratis cloud-baseret platform, der hjælper ingeniørteams med at samarbejde og administrere, se og dele Computer-Aided Design (CAD) filer. NASA Tournament Lab håndterer udfordringen, som understøtter NASA Innovative Advanced Concepts (NIAC) undersøgelse af HOEE-konceptet. Udfordringen er en del af NASA's Prizes, Challenges, and Crowdsourcing-program, overvåget af NASA's Space Technology Mission Directorate (STMD).

Til dato er de fleste kendte exoplaneter blevet bekræftet gennem indirekte metoder. Disse omfatter Transit Method (alias Transit Photometry), hvor periodiske fald i en stjernes lysstyrke bruges til at detektere tilstedeværelsen af ​​en eller flere planeter, der passerer foran den (transiterende) i forhold til observatøren. En anden er Radial Velocity Method (alias Doppler Spectroscopy), hvor bevægelsen af ​​en stjerne frem og tilbage (i forhold til observatøren) bruges til at bestemme gravitationspåvirkningerne, der virker på stjernen (dvs. et system af planeter).

Når de bruges i kombination, er disse metoder meget effektive til at begrænse størrelsen og omløbsperioden for exoplaneter (Transitmetode) og deres respektive masser (Radial Velocity Method). Men med næste generations instrumenter som James Webb Space Telescope (JWST) kan astronomer udføre Direct Imaging-undersøgelser af exoplaneter. I dette tilfælde fanges lys fra fjerne exoplaneter direkte og analyseres med et spektrometer. De opnåede spektre kan give data om en planets overflademineraler og bestemme tilstedeværelsen af ​​oceaner, kontinenter, vejrsystemer, vegetation og de gasser, der udgør dens atmosfære.

Disse data vil gøre det muligt for astronomer og astrobiologer at karakterisere exoplaneter og trygt sige, om en planet er "beboelig" eller ej. En vigtig del af denne metode er coronagraph, et instrument, der blokerer for blænding fra forældrestjerner, så lyset, der reflekteres fra exoplanetatmosfærer, kan visualiseres og scannes ved hjælp af spektrometre for at bestemme den kemiske sammensætning. Sagde Dr. John Mather, en senior astrofysiker ved NASAs Goddard Space Flight Center og en senior projektforsker for JWST:

"The hybrid observatory might help us answer some of the most pressing questions about extraterrestrial life. Observing many systems would help answer the question of why configurations like our own are rare and why none is quite like home. It is truly exciting that the public can be part of this revolutionary effort. I can't wait to see what ideas they bring to the table."

The key to the HOEE is the "Starshade" spacecraft, a concept introduced by the Habitable Exoplanet Observatory (HabEx) at NASA JPL back in 2016. Initially, it was thought that only space telescopes like the James Webb and the Nancy Grace Roman Space Telescope (RST) could benefit from a starshade-type spacecraft. But with the HOEE concept, ground-based telescopes that fall into the 30-meter-class (~100 ft) range could also conduct Direct Imaging surveys. This includes next-generation observatories like the Extremely Large Telescope (ELT), Giant Magellan Telescope (GMT), and the Thirty Meter Telescope (TMT).

For the Ultralight Starshade Structural Design Challenge, NASA is looking for ideas for a lightweight starshade that could accomplish that very task. According to NASA, the goal of this challenge is to develop an "innovative low-mass starshade structure that could meet the mass, shape, strength, and stiffness requirements." Participants are free to choose from four suggested designs (or a hybrid thereof), which include:

1. Ultralight version of the current JPL HabEx concept
2. Umbrella with petals
3. Rigidizable inflated structure
4. Truss-based structures

The ideal design, they state, will allow for compact packaging and successful deployment once in Earth's orbit. In other words, it must be able to collapse and fold up so the spacecraft can fit inside a rocket payload fairing, then unfurl once it reaches space. This is similar to what engineers accomplished with James Webb, especially where its primary mirror and sunshield were concerned. They also stress that it must have the lowest possible mass to be easier (and cheaper) to launch, that its chemical thrusters can keep it aligned during observations, and change its orbit to observe different targets.

These and other details (including orbital distance and the starshade's diameter) are specified on the challenge page:

"An orbiting starshade (170,000 km away) could cast a shadow of the central star without blocking the reflected light from its planets. So that it can be used with the largest ground-based telescopes, the starshade needs to be 100 m in diameter. This large structure must be tightly packaged so that it can fit inside the fairing of a large rocket (e.g., Falcon Heavy or Starship).

"It must also have the lowest possible mass so that chemical thrusters can keep it aligned during observations and solar electric propulsion system can change its orbit to observe many targets. NASA seeks breakthrough mechanical/structural concepts for a deployable, low mass, high stability, and high stiffness starshade structure."

In order to be eligible for this challenge, participants must either be U.S. citizens or from an eligible country (specified here). The top five submissions will share a prize purse of $7,000. The full list of the competition requirements and all relevant information and documentation are posted on the GrabCAD challenge page. + Udforsk yderligere

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