advances.sciencemag.org/cgi/content/full/3/1/e1601992/DC1

Supplementary Materials forPure iron grains are rare in the universe
Yuki Kimura, Kyoko K. Tanaka, Takaya Nozawa, Shinsuke Takeuchi, Yuko Inatomi
Published 18 January 2017, Sci. Adv. 3, e1601992 (2017)
DOI: 10.1126/sciadv.1601992

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Supplementary Text
fig. S1. Time evolution of the acceleration gravity in the sounding rocket during
the microgravity experiment.
fig. S2. Photographs of the experimental systems.
fig. S3. Examples of nucleated particles in a microgravity environment.
fig. S4. Images of interference fringes during the Fe nucleation experiment undermicrogravity.

Supplementary Text
Experimental System and Procedure
The nucleation chamber (n in fig. S2A) was a 150-mm-long stainless-steel cylinder with an internal
diameter of 65 mm. It was equipped with two viewports for recording the paths of interference fringes of
the two lasers, and one viewport for measuring the temperature of the evaporation source using apyrometer (ISQ5-LO, Hazama Sokki Co. Ltd., Yokohama). Two ports were also equipped with a 0.1mm-diameter chromel–alumel thermocouple [a combination of WF-1/8"PT -0.8-2-T -TK-1000 mm/150mm (Tecsam Co. Ltd., Hsinchu) and KMT-100-100-050 (ANBE SMT Co., Yokohama)] for measuring
the temperature at the end of the evaporation source as an alternative method for determining thetemperature of the evaporation source. Two electrodes (PF-SM6-3KV-10A, Kawaso Texcel Co., Osaka)
were used for heating the evaporation source. The chamber also had a specially coordinated highresolution pressure gauge (HAV-60KP-V; Sensez Co., Tokyo). The accuracy of pressure measurement
was ±90 Pa, which corresponds to an accuracy of ±1.5 K at the nucleation temperature (~900 K) given
by our experimental results. A quarter-inch stainless steel tube (g in fig. S2A) was connected to avacuum system through a valve (6LVV-DPBW4-P1; Swagelok Co., Manchester; va in fig. S2B) for
evacuation and the introduction of gas. The air in the chamber was evacuated by a combination of aturbo-molecular pump (TG50F, 50 L/s; Osaka Vacuum, Ltd.) and a scroll-type dry vacuum pump (DIS90; ULVAC Kiko Inc., Saito City). After a sufficient vacuum was attained (pressure 10-5 Pa), pure Argas (>99.9999% purity) was injected into the chamber. The Ar buffer gas was essential for measuring
the partial pressure and temperature of evaporated Fe gas based on the shifts of interference fringes of
optical lasers at two different wavelengths (see below). In addition, the inert Ar gas decreased the mean
free path and shortened the cooling timescale of the evaporated Fe gas, which allowed us to perform thenucleation experiments within the short duration of the microgravity environment and within the limited
space available in the rocket. To observe the effects of the Ar gas pressure on the results, the twonucleation chambers with identical configurations were installed in the rocket (fig. S2B) and each was
filled with Ar gas at a different pressure (2 × 104 Pa and 4 × 104 Pa).
The Mach–Zehnder-type interferometer (fig. S2A) had two lasers: a polarized green laser with awavelength G = 532 nm (compact green laser module, 10 mW BEAM MATE HK-5616; ShimadzuCorp., Kyoto) and a red laser with a wavelength R = 635 nm (4.5 mW continuous wave circular beamlaser diode module; Edmund Optics Inc., Barrington, NJ). The evaporation source, a Fe wire (0.1mm × 100 mm) wrapped around a tungsten filament (0.3 mm × 68 mm), was carefully aligned
parallel to the optical path (<4 × 10–4 rad) and was made as long as possible to obtain a high column
density of evaporated Fe gas. This enabled us to detect tiny changes in the refractive index of as little as
1.0 × 10–6, which corresponds to a change in temperature from 298 K to 301 K for Ar gas at 2 × 104 Pa.
Because the vapor pressure of metallic tungsten is much lower (10–5 Pa at 2508 K) than that of Fe(9.7 × 104 Pa at 2508 K), the partial pressure of evaporated metallic tungsten could be neglected during
our experiments.
The interference fringes of the green and red lasers were captured by a recording system (Board Camera
MS-88HCS without a low-pass filter; Moswell Co., Ltd., Yokohama) and were downloaded to theground by telemetry at a rate of 10 frames per second during the experiment. The spatial resolution was~45 m.

Launch of sounding rocket S-520-28
Sounding rocket S-520-28 of the Japan Aerospace Exploration Agency (JAXA) was launched at 4 pm
JST on December 17th, 2012, and reached an altitude of 312 kilometers 283 seconds after liftoff. The
mean gravitational acceleration during the parabolic flight, measured by a triaxial analogue
accelerometer module (Model 2470-002; Silicon Designs Inc., Kirkland, WA) placed on a base plate of
the nucleation chamber was (6.3 ± 0.8) × 10–4 G (fig. S1), which is two orders of magnitude lower thanthat in microgravity experiments performed aboard aircraft. The duration of the microgravity was asmuch as ~445 seconds in this sounding rocket, much longer than the ~20 seconds achievable in aircraft.
Such relatively long and better microgravity condition allowed us to perform two successive nucleation
experiments at different Ar gas pressures (after waiting for residual convection to settle down) in asingle flight. The rotational frequency of the rocket was kept as low as –0.018 Hz. Electrical heating of
the evaporation sources in Ar gas at an initial pressure of 2.0 × 104 Pa (4.0 × 104 Pa) was performed for
65 seconds in total by constant elevation of the applied voltage (~0.13 V s-1) between 180 and 240
seconds (255 and 315 seconds) after the launch, and at constant voltage at 8.6 V for the subsequent 5seconds.

fig. S1. Time evolution of the acceleration gravity in the sounding rocket during the microgravity
experiment. Labels A to I indicate the following events: A, before launch; B, launch; C, termination ofignition; D, despinning by spreading of yo-yo; E, opening of the nose cone for release of heat; F,experiment in Ar gas at 2.0 × 104 Pa; G, experiment in Ar gas at 4.0 × 104 Pa; H, transfer of the recorded
images to the ground; and I, termination of parabolic flight. The gravitational acceleration was measured
by a triaxial analogue accelerometer module positioned on the base plate of the experimental system. Itwas same order in three axes during parabolic flight.

fig. S2. Photographs of the experimental systems. (A) Top view of the double-wavelength Mach–Zehnder-type laser interferometer with the nucleation chamber. Red and green arrows show the opticalpaths of red and green lasers, respectively. (B) Side view of the experimental systems. View directionsof the upper and bottom systems are from bottom and top of A, respectively, i.e., each system is 180o
opposite in phase. Labels indicate: b, beam splitter; c, collimator; d, dichroic mirror; e, electrode; g, gasline; i, interface connecters; l, lens; m, mirror; n, nucleation chamber; p, polarizer; q, Quick-Connect; s,short-pass filter; v, vacuum gauge; cam, CCD camera; gl, green laser; rl, red laser; py, pyrometer and va,valve. Evacuation of the air and subsequent injection of Ar gas into the chamber were performed on theground after the experimental system had been installed inside the rocket.

fig. S3. Examples of nucleated particles in a microgravity environment. (A) Real images obtained inanother nucleation experiment of tungsten oxide during a parabolic flight of an aircraft of Diamond Air
Service Inc., Japan. These images are shown to illustrate the existence of concentric nucleation aroundthe entire evaporation source, which cannot be confirmed from the images of the interference fringes
because the view direction is parallel to the evaporation source. The nucleated particles are illuminatedby the hot evaporation source. Because the evaporation temperatures of Fe were very high, the brightevaporation source and the darker nucleated particles could not be recorded simultaneously due to thelow dynamic range of our general camera. Tungsten oxide evaporates at a much lower temperature(~1200 K) than does Fe (~2000 K), permitting observation of its nucleated particles. The number in each
image shows the time in seconds. The image in the upper left (labeled as 0) corresponds to an image
recorded just before the appearance of nucleated particles. (B) Photograph of the chamber for themicrogravity experiment in the aircraft from the same viewing direction as the panel A. (C) Schematicof the evaporation source and a smoke composed of nanoparticles. The smoke forms a concentric
cylinder around the filamentary evaporation source because of symmetrical diffusion of the evaporated
gas under microgravity.

fig. S4. Images of interference fringes during the Fe nucleation experiment under microgravity.
Color-separated images of the interference fringes in Fig. 2 for the red laser (A–C) and the green laser(D–F) at an initial Ar buffer gas pressure of 4 × 104 Pa: (A, D) before heating of the evaporation source,(B, E) 0.4 s before the nucleation of Fe grains and (C, F) at the time of nucleation. In C and F, the dottedline in the upper right corner indicates the nucleation front of the Fe grains, above which interference
fringes disappear due to scattering of light by abundantly formed Fe grains. Panel (G) shows time-series
images of the interference fringes indicated by white lines in A and D. Horizontal and vertical axes in
the panels correspond to the time and position from x1 to x2, respectively. Labels es show the position of
the evaporation source. The dotted white line in G shows the time of nucleation. The scale bar in C
corresponds to 3 mm.