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Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

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Page 1: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

Optical Interferometry in Space

Gerard van Belle, Lowell Observatory

Space Astrophysics Landscape for the 2020s and Beyond

Page 2: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry2

The Need for

Angular

Resolution

Paul Signac, “Antibes, die Türme”, 1911

Page 3: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry3

Spatial Resolution Advances Science

Example: Planetary science

Is the surface old or new?

Implications for population &

dynamics of Kuiper Belt

Variations in surface morphology

Chemical composition

Seasonal variations in the surface?

Evidence for plate tectonics?

Page 4: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry4

Heliophysics Best example: observations of the sun

Roughly 1,000,000 closer than any other star

SOHO observations of the Sun

Interesting structure Sun spots Phlages Prominences Mass ejections

Interactions with the surrounding environment

Wish to extend these observations to other stars Conversely, other stars will inform us about

the sun

Page 5: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry5

(12 m)(2.4 m)

Extragalactic

Page 6: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry6

Our Science Menu

From the near to the

distant

Blue = bright

Red = faint

Page 7: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry7

Our Science Menu

From the near to the

distant

Blue = bright

Red = faint

Page 8: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry8

Current State of

the Art

Page 9: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry9

Page 10: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry10

Under

construction

Page 11: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry11

Under

construction

Page 12: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry12

Under

construction

Current resolution

leader: CHARA Array

(330m resolution in

visible, NIR; 6x1m)

Current sensitivity

leader: VLTI (130m

resolution in

NIR, MIR; 4x8.4m)

Page 13: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry13

Science Enabled by Extreme Resolution

Still interesting things to learn

about bright objects

Stellar surface imaging

Limb darkening: upper stellar

structure

Spot mapping: convection

physics, magnetic field strength

and persistence

2.5 mas

Page 14: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry14

Imaging: Stars are Photogenic The past 10 years

Parametric modeling at first, and nowadays Direct imaging

Already starting to see some surprises Stellar structure not as expected from simple

models, particularly gravity darkening Nearly 1/6 of all Astro2020 Science WPs

concern stars

CHARA-MIRC Images of Rapid Rotators: Monnier+ 2007, Zhao+ 2009, Che+ 2011

Page 15: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry15

VLTI-GRAVITY

Observations of Sgr A* at

the Milky Way center

S2 passes within 1,400

Schwarzschild radii

Mass: ~10 M

Speed: 2.5% c

Acceleration: 1/6 gee

A unique strong-gravity

laboratory

1515

Gravity Collaboration,

Abuter+ 2018a

15

JWST

Diffraction

Limit

(77mas)

Page 16: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry16

Departure from Newtonian Dynamics

Gravity Collaboration, Abuter+ 2018a

Gravitational

Redshift

Page 17: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry17

Exoplanets

HR8799e spectrum from VLTI-

GRAVITY

Lacour et al. 2019 A&A 623 L11

Ja

so

n W

ang

Page 18: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

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Imaging Exoplanet Transits

NPOI & CHARA, other facilities

can observe exoplanet transits

Planet’s shadow is ‘perfect’ star

spot

λ-specific observations

atmospheric composition

Extreme challenge: needs very

high signal-to-noise

HD189733 predict:

van Belle 2008

Venus

Page 19: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

Dr. van Belle’s Patented Six-Slide

Crash Course in Interferometry

You too will be an expert in 180 seconds

Page 20: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry22

The Telescope: What’s Happening Inside?

Our parallel rays enter and bounce around – in a very special way

Every path of every ray from

the star traces the same

pathlength through the

telescope

Page 21: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

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The Telescope: What’s Happening Inside?

When light rays from a source satisfy

this pathlength condition, the can

form an image

This is an ‘interference

phenomenon’

Special secret: all telescopes

are interferometersInterference

is why ‘point-like’stars appear as

Airy disks

(though thiseffect is usuallywashed out bythe atmosphere)

Page 22: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry24

The Telescope: What’s Happening Inside?

This pathlength condition is

true for other nearby stars in the

field of view of the telescope, at

slightly different angles

This dictates the very special

shape of the mirrors

Page 23: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry25

The Telescope: What’s Happening Inside?

Screw this up?

You get Hubble:

Mirror missed spec by 2000×

Page 24: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

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In the Pursuit of Clever (at the risk of Stupid)

Here’s a neat trick: satisfy the pathlength

condition with separate pieces of glass for your

primary mirror

Examples: Keck, GTC, E-ELT, TMT, GMT

Keck ‘hex’ PSF

Page 25: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

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Cracking the Resolution Problem

Taking the neat trick even further:

really chop up your telescope into a

long baseline interferometer

This works as long as some light is

getting to the back end, and if the

pathlength condition is met

Can make the ‘diameter’ very big

Page 26: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry28

Cracking the Resolution Problem

Taking the neat trick even further: really chop

up your telescope by making it many

telescopes

(Still have to satisfy the pathlength condition)

Viola! High spatial resolution

NB. for greatest sensitivity in the optical, one must

mix-then-detect; for radio, detect-then-mix is OK

Page 27: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

~ Thus Concludes the Lesson ~

Page 28: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry30

Interferometry

from Space

Paul Signac, “La Corne D'or, Les Minarets”, 1907

Page 29: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry31

SIM: The Elephant in the Room?

Space Interferometry Mission

Specifically endorsed in 1990, 2000

decadals

Specifically un-endorsed in 2010

decadals

An astrometric mission that

happened to use interferometry

Page 30: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

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Mechanical Tolerances

Simple imaging far easier than astrometry, GWs

Even easier than single-aperture work in certain regards

Mission

Physical

scale units

Mechanical

Precision units

Dynamic

range ratio task

Optical Precision during an observation

Imaging

Interferometer100 m 30 nm 3.33E+09 1 imaging / spectroscopy

SIM 10 m 50 pm 2.00E+11 60 astrometry

LISA 2500000 km 20 pm 1.25E+20 3.75E+10 grav. waves

Mechanical stability during an observation

Imaging

Interferometer100 m 1 cm 1.00E+04 1 imaging / spectroscopy

JWST 6.5 m 32 nm 2.03E+08 20313 imaging / spectroscopy

Page 31: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

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Space >> Ground

Effects of atmospheric

turbulence

Coherence time: 1ms versus

10-1,000sec

Atmospheric vs. instrumental

Chaotic vs. predictable

Small space-based apertures

quickly win over larger

ground-based ones

Object:

constant

Atmospheric

turbulence:

1-10ms time

scales

Ground-based telescopes

stuck in the soup

Untrackable

spacecraft

disturbance:

10-1,000s

time scales

Page 32: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry34

Baby Steps

Simple space interferometer

Based on 2×10m manufactured booms, visible operations (non-cryogenic)

Small apertures (2”) easily more sensitive than CHARA, NPOI (1 meter!)

Made In Space

Optimast-SCI

SBIR Phase I study

Page 33: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry35

Interstellar Asteroid Oumuamua

Page 34: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry36

ISS Additive

Manufacturing First, second generation of

additive manufacturing printers

are aboard ISS

Commercial fiber

manufacturing experiment also

on-board

Further developments

‘Extended structure’

manufacturing

Thermal/vac demonstrated

Page 35: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry37

0.1

1.0

10.0

100.0

1,000.0

10,000.0

0.1 1.0 10.0 100.0 1,000.0 10,000.0

Size

(m

)

Wavelength (microns)

Mid-IR: Achieving 0.1” Resolution

telescope diameter (m) max interferometer baseline (m)

5 m

UV/Vis/NIR

Mid-IR/Far-IR/Sub-mm mm/radio SPIRIT

Herschel

Breaking the Confusion Limit

Page 36: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry38

ISO

HERSCHEL

SPIRIT

HH30

Above: Observable water that forms in regions of

protoplanetary disks, where temperatures are well below

1000 K. SOFIA/HIRMES will have access to all the water

lines shown, including the 25.9 μm line (yellow), the only

one accessible to JWST. However, without corresponding

spatial resolution, the origin of these lines can only be

inferred from disk modeling.

Left: Hubble image of HH30 compared to 100 μm beam

sizes

Water in Protostellar Disks

Page 37: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry39

After the Easy Things

Experience base built up with

imaging missions can lead to

Example: nulling, for planet

spectroscopy

Page 38: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry40

Why Does NASA Care?

Virtually all missions discussed in the 2015 ‘Enduring Quests Daring Visions’ report are interferometric in nature

These tools are needed to establish the fundamental nature of the cosmos

NASA will need a workforce that can plan, design, implement, and use these facilities

Page 39: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry41

Going from Science Fiction to Science

Image credit:

Made In Space

Page 40: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry42

Carpe Posterum: Exo-Earth Mapper1 pixel 10×10

100km3×325km baseline

30×30250km

100×1001000km

300×300

Page 41: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry43

Recommendations

Challenge to interferometry community

Propose Explorer and Probe-class missions in the 2020s,

motivated by the science

Demonstrate the slam-dunk science from long-baseline

interferometry

Challenge to NASA

Based on their merits, select those missions!

Support and (re-)build the interferometry community in

anticipation of 2030 Flagships – including ExoEarth Mapper

Page 42: Optical Interferometry in Space - USRA-Houston€¦ · Optical Interferometry in Space Gerard van Belle, Lowell Observatory Space Astrophysics Landscape for the 2020s and Beyond

2019 April 2G van Belle, Lowell - Optical Interferometry44

Questions?

Paul Signac, “Port St. Tropez”, 1899