Research

"We support astronomy for the same reason we support a symphony orchestra, or an opera, or a poet. Because it distinguishes us as human." Bart Bok

Magnetic Field Characterization

The knowledge of exoplanetary magnetic fields provides valuable insights into the planet's interior structure, atmospheric escape, atmospheric dynamics, formation history, and habitability.

Radio Emission Observations

One of the most promising methods to detect exoplanetary magnetic fields is to study their auroral radio emission.

Involvement in space-based radio missions

ROLSES-1

(Radiowave Observations at the Lunar Surface of the photoElectron Sheath)

ROLSES-1 launch is scheduled for Feb 2024!
Exoplanet science advisor

ROLSES-2

(Radiowave Observations at the Lunar Surface of the photoElectron Sheath)

ROLSES-2 launch is scheduled for 2026!
Exoplanet science advisor

LuSEE-Night

(Lunar Surface Electromagnetics Experiment-Night)

Launch scheduled for 2026
Exoplanet science advisor

FarView

(A Lunar Far Side Radio Observatory)

Under-development (Phase 2)
~2030s deployment
Exoplanet science advisor

LCRT

(Lunar Crater Radio Telescope)

Under-development (Phase 3)
~2030s deployment
Exoplanet science advisor

HADES

(A SmallSat Mission to Characterize Radio Foregrounds in the Lunar Environment)

Under-development.
~2027 launch
Team member

Go-Low

(Great Observatory for Long Wavelengths)

Under-development.
~2027 launch
Go-LOW will perform the first survey of exoplanetary magnetic fields within 5 parsecs including the potentially habitable planet Proxima b.
Team member

FARSIDE

(A Low Radio Frequency Interferometric Array on the Lunar Farside)

~2030s deployment
FARSIDE will be able to study the magnetic fields of exoplanets within ~80 light-years including the nearest habitable planets.
Exoplanet science committee

The first possible detection of an exoplanet in the radio (Turner et al. 2021)
- We tentatively detect circularly polarized bursty emission from the tau bootis system in the range 14-21 MHz with a flux density of ~890 mJy and with a statistical significance of ~3 sigma.
- We also tentatively detect slowly variable circularly polarized emission from tau Bootis in the range 21-30 MHz with a flux density of ~400 mJy and with a statistical significance of >8 sigma. The slow emission is structured in the time-frequency plane and shows an excess in the ON-beam with respect to the two simultaneous OFF-beams. See the figures below.
- Further observations are required to confirm this possible first detection of an exoplanetary radio signal.
- Follow-up observations are underway (Turner et al. 2023, Turner et al. 2024)

Fig. Time-series shows an excess signal in the ON-beam compared to the OFF beams (Turner et al. 2021)

Fig. Integrated spectra shows an excess signal in the ON-beam compared to the OFF beams (Turner et al. 2021)

- CO-I on the "Exoplanets and Stars" Key Science Program for the NenuFAR telescope. Awarded up to 1000 hrs/per semester
  - Published the 1st exoplanet observation with NenuFAR (Turner et al. 2023)

- Searching for exoplanet radio emission using LOFAR (16 - 76 MHz) in beamformed mode
  - Created the BOREALIS pipeline to analyze this data (Turner et al. 2017, Turner et al. 2019a)
  - Preliminary results on the non-detection of 55 Cnc can be found in Turner et al. 2017.
  - Used Jupiter LOFAR observations scaled such that it simulates exoplanetary radio emission to accurately quantify the sensitivity of LOFAR LBA beam-formed observations (Turner et al. 2019a)

Fig. Stokes-V Dynamic Spectra of Jupiter LOFAR beam-formed observations (Turner et al. 2019a)

Observed with VLA P-band (250 MHz) the secondary eclipse of close-in transiting exoplanets
Part of the VLA VLITE team looking for 236-492 MHz emission from exoplanets

Near-UV Asymmetries

We have observed 19 targets in the near-UV from the ground. All have resulted in non-detections of asymmetries.
- All targets are published (Turner et al. 2013, Pearson et al. 2014, Zellem et al. 2015, Turner et al. 2016b, Turner et al. 2017).

WASP-77Ab near-UV transit (Turner et al. 2016b)

Used the plasma photoionization and microphysics code CLOUDY to explore whether there is a UV absorbing species that can cause an early UV ingress in the transits of exoplanets due to the presence of a bow shock compressing the coronal plasma.
- We find that optical depths are orders of magnitude too small (~3x10−7) to explain the ∼3% UV transit depths seen with Hubble.
- We conclude that the likely cause of the observed near-UV early-ingress is an escaping planetary atmosphere
- Our conclusions are consistent with other studies suggesting that UV asymmetry observations are not a suitable approach for detecting exoplanet magnetic fields
- The paper can be found here: Turner et al. (2016a)

Atmospheric Characterization

High-Resolution Observations

- Detected ionized calcium (Ca II) and H-alpha in the atmosphere of the ultra-hot Jupiter KELT-9b (Turner et al. 2020)
- We derived the physical conditions the lines formed under:
  - Ca II is formed at a radius of 1.2 Rp where the H-alpha is formed at a radius of 1.33 Rp.
  - Temperature between 6100 K and 8000 K

Fig. H-alpha and ionized calcium detections in the atmosphere of KELT-9b (Turner et al. 2020).

- I'm the PI of the ExoGemS large survey on Gemini-N and Gemini-S (2020-2024) to explore the diversity of planetary atmospheres at high-resolution.
- Our first result from ExoGemS was the detection of Ca II and sodium in the atmosphere of the ultra-hot Jupiter WASP-76b (Deibert et al. 2021).
- Detected chromium hydride, a robust tracer of atmospheric temperature, for the first time in an exoplanet atmosphere at high-resolution (Flagg et al. 2023).

Fig. Ionized calcium detections in the atmosphere of WASP-76b (Deibert et al. 2021).

Ground-based Near-UV Observations

Constrained the near-UV to optical spectrum of transiting exoplanet using ground-based photometry:
- Super-Earth GJ 1214b, 25 hot Jupiters, and 1 hot Neptune: (Teske et al. 2013, Zellem et al. 2015, Turner et al. 2017, Turner et al. 2016b)
First detection of a smaller near-UV transit depth than that measured in the optical in WASP-1b (Turner et al. 2016b).
Smaller blue-band transit depth than near-IR in HAT-P-37b, suggestive of TiO in its atmosphere (Turner et al. 2017).

Fig. Transit depth variation vs wavelength for WASP-1b (Turner et al. 2016b). The smaller near-UV transit indicates TiO in its atmosphere.

Atmospheric Modeling

Finding new sources of opacity in exoplanet upper atmospheres
- Modeled planetary gas in radiative and thermal equilibrium with the stellar radiation field with CLOUDY.
- Promising sources of opacity from the X-ray to radio wavelengths are found, some of which are not yet observed.
- Paper can be found here: Turner et al. (2016a)

Fig. Transit depth for radio wavelengths for the CLOUDY modeling of the escaped planetary gas in thermal equilibrium with the radiation field.

Exoplanet Orbital Evolution

Confirmed that the ultra-hot Jupiter WASP-12b's orbit was decaying (Turner et al. 2020b)
- Confirmed with the transit and occultation timing data from TESS that the orbit of WASP-12b is decaying
- We find an orbital decay timescale of 3 million years
TESS observations of the hot Jupiter WASP-4b show signs of TTVs (Turner et al. 2022)
- We find that the TTVs of WASP-4b cannot be explained by the second planet but can be explained with either a decaying orbit or apsidal precession, with a slight preference for orbital decay
Examined TESS observations of the hot Jupiter XO-6b (Ridden-Harper et al. 2020)
- We found no evidence of transit timing variations as was indicated by ground-based observations
- Our findings highlight TESS's capabilities for robust follow-up, and confirm that TTVs are rarely seen in hot Jupiters, unlike is the case with small planets.

Fig. Transit timing variations. These variations indicated a decaying orbit for WASP-12b (Turner et al. 2020b)

Discovering New Exoplanets

Fig. RV measurements of the WASP-4 system show evidence of a new planet (Turner et al. 2022)

Discovered the most widely separated companion (WASP-4c) of a transiting hot Jupiter to date (Turner et al. 2022)
- We find evidence of a possible additional planet in the WASP-4 system, with an orbital period of ~7000 days and a mass of 5.47 MJup
- The transit timing variations of all of the WASP-4b transits cannot be explained by the second planet

Titan

Studied Titan's atmosphere and surface using Cassini VIMS observations:
- Discovered the first ever methane lake on the equator of Titan (Griffith et al. 2012)
- Detected an ice-rich linear feature of bedrock, which extends a length equivalent to 40 per cent of Titan’s circumference (Griffith et al. 2019)

Images of the first methane lake on Titan (Griffith et al. 2012).

Composition map of Titan. Blue pixels indicate ice-rich regions while the green, red, orange and brown pixels indicate diverse ice-poor regions (Griffith et al. 2019).