3 Night Side
JPL, Pasadena · Monday, 15 May – Tuesday, 23 May 2028.
Glen’s forward landed at 15:42 on Monday, while Dana was losing an argument with Horizons about which frame she had asked for.
| From | Glen Farris |
| Sent | Mon 15 May 2028 15:42 PDT |
| Subject | FW: ESA-ESOC-PDO-TN-2028-017 (draft, rev 3) |
INTERNAL HEAT SOURCE!! Somebody in Darmstadt has been reading Arthur C. Clarke. Bring it Thursday, we'll do a dramatic reading.
ESA-ESOC-PDO-TN-2028-017, draft, rev 3, 2028-05-09. M. Kessler, R. Albrecht
1. Colour temperature 170–210 K above sunlit models.
2. 5.81 ± 0.03 h; 8 ± 2% in NC1; nothing in the visible (< 0.02 mag).
3. Transients at the infrared minimum (~3σ). Predicted minimum of 6 May confirmed by Surveyor (21:40 UT). One OGS transient within window, none outside.
4. Not explained by solar heating. Possibly calibration of commissioning data (being assessed), unusual surface properties, or a residual internal heat source.
5. Continued monitoring. No public statement.
Glen had put his exclamation marks on the one phrase in the note that had been placed where a reader would skip it. He would do the voice on Thursday, too. He had a voice for ESA documents, a little Werner Herzog, and it always got a laugh from the postdocs.
She read item 3 instead. Glen hadn’t. A prediction, made in advance, by somebody with something to lose, and met. In her experience anomalies did the decent thing when you booked telescope time for them, and went away.
Item 4 she read slowly. It was ranked the way frightened people ranked things: the explanation that cost you nothing first. Calibration of commissioning data, with being assessed in brackets, which meant somebody had been asked and hadn’t answered. Unusual surface properties, which was a drawer you could put anything in, except that nobody beat NEATM by two hundred kelvin with a funny regolith. Then the third one.
Residual.
If you had one temperature and a model and a gap between them, you wrote internal heat source and let people laugh. Residual was a different word. Heat that was left over, and heat that was left over was heat on its way out. You didn’t get that from one epoch. You chose that word because you had watched the number go down, week after week, and you couldn’t bring yourself to call it anything that didn’t say so. There was a curve in Darmstadt, and it wasn’t in the note, and somebody, Albrecht she would bet, the one who wrote the cover letters, had decided it was a curve too many for a draft going to JPL.
Dana had one like it. Hers was a folder on her laptop that the sync client had never been told about, and a square of paper in her bag with a date on it.
She replied to Glen: Fun. Item 3 is the interesting one.
He sent back a thumbs-up and, a minute later, It’s ALL interesting!! Rita wants a call in June, I’m thinking we co-author the orbit.
That week she did the work JPL paid her for in the daytime and the other work after six.
The Surveyor team had started pushing calibrated frames, four visits a day, and the new nights tightened her late fits until the last error bar no longer overlapped the first. Cutting the arc into three had been bad enough. She cut it into five. The plot came up with the units in the corner, × 10⁻⁹ au/d², and five points walking up toward zero:
−1.9 ± 0.5. −1.7 ± 0.4. −1.5 ± 0.25. −1.25 ± 0.2. −1.05 ± 0.2.
The braking was getting weaker. She fit a line and got a slope a little over two sigma from flat. Two sigma on five points was what you got when you wanted something, and she knew exactly how badly she was wanting it, so she spent Wednesday night trying to make it go away. She dropped the first segment. She dropped the last. She inflated every error bar until she’d have been embarrassed to show it. It kept coming back a little over two, and climbing as the nights came in.
The line reached zero in August, with weeks of slop on either side. The slop covered the date in her bag, comfortably.
At eleven on Tuesday night, the 23rd, she was still in her office with the PDF of the technical note open to its last page, where the distribution list gave a direct line for M. Kessler, ESOC, with the country code and everything.
It would be eight in the morning in Darmstadt. She didn’t email Glen. Glen would make it a call with an agenda and Rita on it and a slide about data rights, and by the end of it the only thing anybody would have said out loud was co-author.
She dialed from her cell.
“Kessler.”
“Dr. Kessler, it’s Dana Okafor at JPL. I’m sorry, I know it’s early.”
“It is eight. I am at my desk.” A pause. “Is Glen with you?”
“No.”
The pause after that was long enough for him to understand it.
“You fitted non-gravs,” she said. “On the video call I said ours was the same. It’s not the same anymore. I’ve got it in five segments now, and it’s weakening. The trend’s a little over two sigma.” She heard herself go on. “A line through it hits zero in August.”
It was the first time she had said the month to anyone.
“August,” he said. “I have July. But my arc is shorter. Your arc is longer, and you have Catalina at the front of it. August is probably better.”
He had done it too. Of course he had. Somebody who caught a dozen glints and didn’t trust them would have fit a line through anything that held still.
“You have a cooling curve,” she said.
The line was quiet. She could hear an office on the other end, a door, somebody’s chair.
“Yes,” he said. Keys. “I will send it now.”
It arrived while he was still on the line. Thirteen points, weekly medians of the infrared channel at the cycle minimum, 20 February to 14 May, forty to ninety frames behind each. Every week lower than the last. The thirteenth sat at about 0.82 of the first. She fit it before she had decided to and got −1.5 ± 0.1% a week, with residuals so dull she wanted to take them apart.
“Your first weeks are commissioning data,” she said.
“Yes.”
“Your first four points could be the camera cooling down, not the target.”
“The frames since commissioning say the same.” He had been waiting for that one. “Take out the first four. The slope is the same within the error. I will send that also.”
“Send that also.”
“Now yours,” he said. “Your early segments were not all reduced against the same reference stars.”
“Some were. Not all.”
“Then part of your slope could be the star catalog changing under it.”
“Could be.”
“I can reduce your nights against ours. The same reference stars we use for the ESA frames, all of them, one pipeline. If the slope is still there after, it is not the catalog.” He went on before she could thank him. “And there is a better test. If it is a natural Trojan, it has been at L5 a very long time. It should be in the old surveys.”
“And if it isn’t?”
“Then that is also a result.” Keys again. “I can start this week.”
She looked at the thirteen points. They were too smooth to be a camera.
“Run it back,” she said.
“My model is crude.”
“Run it back anyway.”
“A slab. Conduction inward, radiation outward, sunlight on top. Nothing clever.” He was quiet a moment, looking at the number again before he said it to somebody at JPL. “If I run it backward, a few years ago the outer meters were near the melting point of iron.”
“Impact.”
“I thought so. But an impact that puts that much heat into the surface of a two-kilometer body breaks pieces off. There would be a family. Debris on nearby orbits. Dust, at least. You have looked at it in your stack.”
“A point.”
“A clean point. There is no dust.” He said it as if he had looked for dust for a long time and resented it for not being there.
She wrote no ejecta on the pad beside her keyboard and then didn’t know what to write after it.
“There is one more thing,” Kessler said. “It is not in the note.”
“Rita took it out.”
“Rita would take it out. I did not give her the chance.” He didn’t sound proud of it. “She is right to be careful. She took out less than this, before, and she was right then also.”
“Go on.”
“At a phase angle near sixty degrees, Surveyor sees a crescent of the night side. About a quarter of the hemisphere. It is enough to fit day and night separately, each week. Two temperatures, not one.” He stopped. “The night side is the warmer one.”
“In how many weeks?”
“In all thirteen weekly fits.”
Dana did the arithmetic. 20 February to 14 May. A quarter of the way around the Sun. A rock that didn’t turn at all would still have had the Sun walk a quarter of the way around it in that time, and the warm face would have come into the light. A rock that turned would have shown it sooner. To keep one face dark for a season, something had to be turning it, slowly, a quarter turn in a quarter year, to match.
There was a short list of things that kept one face away from the Sun for a whole season. She knew the first item on it, and the second, and didn’t go further.
“You have a pole solution?” she said, because it was a question with numbers in it. “From the visible?”
“There is nothing in the visible. Less than two hundredths of a magnitude. Only the glints, and eleven glints are not a pole.” He breathed out. In Darmstadt, somebody said his name from a doorway, and he said something short in German, and the door closed.
“Dana,” he said.
“I’m here.”
“It is holding attitude.”