Hvordan NASAs Webb Telescope vil fortsætte Spitzers arv

Når et vindue til universet lukker, en anden vil åbne med en endnu bedre udsigt. Nogle af de samme planeter, stjerner og galakser, vi først så gennem det første vindue, vil dukke op i endnu skarpere detaljer i det, der snart åbner.

NASAs Spitzer-rumteleskop afslutter sin mission den 30. januar, 2020, efter mere end 16 ekstraordinære års efterforskning. Teleskopet har gjort mange opdagelser ud over dets designeres fantasi, såsom planeter uden for vores solsystem, kaldet exoplaneter, og galakser, der blev dannet tæt på universets begyndelse. Mange af Spitzers gennembrud vil blive studeret mere præcist med det kommende James Webb Space Telescope, som forventes lanceret i 2021.

"Vi har en masse nye spørgsmål at stille om universet på grund af Spitzer, sagde Michael Werner, Spitzer-projektforsker baseret på NASA's Jet Propulsion Laboratory i Pasadena, Californien. "Det er meget glædeligt at vide, at der kommer et så kraftfuldt sæt af muligheder for at følge op på, hvad vi har været i stand til at starte med Spitzer."

Både Webb og Spitzer er specialiserede til infrarødt lys, som er usynlig for menneskelige øjne. Men med sit kæmpe guldbelagte berylliumspejl og ni nye teknologier, Webb er omkring 1, 000 gange stærkere. Det kommende teleskop vil være i stand til at skubbe Spitzers videnskabelige resultater til nye grænser, fra at identificere kemikalier i exoplanetatmosfærer til at lokalisere nogle af de første galakser, der blev dannet efter Big Bang.

Ud over dets opdagelser, Spitzer er også en stifinder for Webb i forhold til, hvordan man betjener et teleskop af denne art. For at måle infrarødt lys med høj følsomhed, et teleskop skal være meget koldt. Spitzer har vist ingeniører, hvordan et infrarødt observatorium opfører sig i det store rum, og hvilke temperaturer missionsplanlæggere bør forvente at kæmpe med for Webb.

"At have et stort teleskop i rummet er svært. Men at have et stort teleskop, der er koldt, er meget sværere, " sagde Amber Straughn, stedfortrædende projektforsker for James Webb Space Telescope Science Communications. "Spitzer hjalp os med at lære, hvordan man bedre kan betjene et meget koldt teleskop i rummet."

Med mere end 8, 700 videnskabelige artikler udgivet baseret på Spitzers opdagelser, teleskopet har været et enormt aktiv for astronomer på tværs af en række forskellige discipliner. Mange af disse fristende resultater er modne til at gense med et mere kraftfuldt teleskop, og Webb er klar til at begynde at undersøge dem tidligt i sin mission. Her er et udpluk af Spitzers præstationer, som Webb vil bygge videre på.

Exoplaneter

En af Spitzers mest fantastiske opdagelser var, at der ikke kun er tre, men syv klippefyldte planeter på størrelse med Jorden, der kredser om en lille, svag stjerne kaldet TRAPPIST-1. TRAPPIST-1 er et af de bedst undersøgte planetsystemer bortset fra vores eget, men der er meget mere at lære om det.

Den fjerde planet fra stjernen, TRAPPIST-1e er især interessant, fordi den har en tæthed og overfladetyngdekraft meget lig Jordens og modtager nok stjernestråling til at have temperaturer, der er venlige nok til flydende vand. Webb vil observere denne planet for at få en bedre fornemmelse af, om planeten har en atmosfære og, hvis så, hvad dens kemi er.

Tilstedeværelsen af ​​molekyler som kuldioxid, dominerende på Mars og Venus, ville have betydning for, om en planet kunne have flydende vand og andre beboelige forhold. Webb vil være i stand til at detektere atmosfærisk vand, også. Derudover Webb vil søge efter varme, der kommer fra TRAPPIST-1b, planeten tættest på sin stjerne.

"Mangfoldigheden af ​​atmosfærer omkring terrestriske verdener er sandsynligvis hinsides vores vildeste fantasi, " sagde Nikole Lewis, assisterende professor i astronomi ved Cornell University i Ithaca, New York. "Det vil være meget nyttigt at få information om luft på disse planeter."

WASP-18b er en anden spændende planet, som Spitzer undersøgte, og som Webb vil undersøge nærmere i observationer tidligt i missionen. Denne gasgigant, med 10 gange Jupiters masse, er placeret ekstremt tæt på sin stjerne, at gennemføre en bane en gang hver 23. time. På grund af dens høje temperatur - hele 4, 800 grader Fahrenheit (2, 650 grader Celsius) - og stor størrelse, det er kendt som en "varm Jupiter." Ved at bruge data fra Spitzer og Hubble, astronomers figured out in 2017 that this planet has a lot of carbon monoxide in its upper atmosphere and little water vapor. This planet is particularly interesting because it's so close to its star that it's in danger of being torn apart completely, and it may not survive another million years. Astronomers are interested in using Webb to look at the processes happening in this planet's atmosphere, which will provide insights into hot Jupiters in general.

Spitzer has also delivered unprecedented weather reports for exoplanets. I 2007 it made the first-ever map of the surface of an exoplanet, the hot Jupiter HD 189733b, showing its temperature variations and cloud tops. For nylig, in 2016, Spitzer highlighted the climate patterns of 55 Cancri e, a possibly lava-covered world more than twice the size of Earth. But maps from Spitzer have given scientists a lot to think about as they look to further investigations with Webb.

Other Exotic Objects

Spitzer has also made strides in identifying and characterizing brown dwarfs. A brown dwarf is larger than a planet but less massive than a star, and while stars generate their own energy by fusing hydrogen, brown dwarfs do not. Spitzer has been able to look at the clouds in brown dwarf atmospheres and observe how they move and change shape with time. Webb will also examine brown dwarf cloud properties and delve deeper into the physics of these mysterious objects.

Infrared light has also been revolutionary for looking at disks of gas and dust orbiting stars, and both Spitzer and Webb are sensitive to the infrared glow of this material. Disks that Spitzer has studied contain the raw materials for making planets and may represent the state of our solar system before Earth and its neighbors formed. Spitzer has seen particles around young stars beginning to transform into the seeds of small planetary bodies, and that some disks have materials similar to those seen in comets in our solar system. Webb can look at the same disks and find out even more about the planetary formation process.

Oodles of Galaxies

As light travels from distant objects to Earth, its wavelength becomes longer because the universe is expanding and those objects are moving farther from us. Just like the sound of a siren seems to lower in pitch as an ambulance drives away, light from distant galaxies also lowers in frequency, a phenomenon called "redshift." That means stars that give off visible light in the early universe will appear in the infrared by the time their light reaches Earth. This makes infrared light an especially powerful tool for exploring the universe's ancient past.

Pinpointing hundreds of billions of galaxies is currently impossible, but Spitzer has made large galaxy catalogs that represent different slices of the universe, containing some of the most distant galaxies we know. The large survey areas of Spitzer and Hubble Space Telescope have allowed astronomers to efficiently look for objects that could be studied in further detail with Webb.

For eksempel, Spitzer, together with Hubble, took an image of a galaxy called GN-z11, which holds the record for most distant galaxy measured yet. It is a relic from when the universe was only 400 million years old, just 3% of its current age and less than 10% of its size today.

"Spitzer surveyed thousands of galaxies, mapped the Milky Way and performed other groundbreaking feats by looking at large areas of the sky, " said Sean Carey, manager of the Spitzer Science Center at Caltech/IPAC in Pasadena, California. "Webb won't have this capability, but it will revisit some of the most interesting targets in the Spitzer surveys to reveal them in amazing clarity."

What's more, Webb's higher sensitivity will allow the telescope to look for galaxies dating back even earlier in the universe. And questions still abound about these distant galaxies:Are there a lot of stars forming in them or relatively few? Are they rich in gas or poor? Are there black holes at their centers, and how do those black holes interact with stars? Og, scientists have pondered a chicken-and-egg problem for decades about which came first:the black hole or the surrounding galaxy?

"We'll be able to see some of the earliest galaxies to form in the universe that we've never seen before, " said Straughn.

Closer to home, Spitzer also studied many examples of a mysterious kind of galaxy called a luminous infrared galaxy, or LIRG. Such galaxies are generating tens to hundreds of times more energy per second than a typical galaxy, and most of that energy takes the form of far-infrared light. Scientists have used Spitzer to study LIRGs and learn about star formation and the growth of black holes during periods of rapid evolution when galaxies collide and merge. Such collisions were even more common 6 billion to 10 billion years ago and influenced the evolution of the universe as we know it.

"Webb will take inspiration from Spitzer and examine a variety of nearby and distant LIRGs to learn more about the role of galactic mergers, bursts of star formation and the growth of supermassive black holes in galactic evolution over cosmic time, " said Lee Armus of Caltech, who will lead a LIRG observing program for Webb.

Into the Infrared Unknown

For more than 16 years, Spitzer mapped out many of the most pressing questions in infrared astronomy. Now it's up to Webb to revisit them with sharper vision, through the grandest window yet to the cosmos.